Maybe the World Cup Wasn’t the Best Example

In our recent New York Times column, we talked about what makes people good at what they do.

As one example, we conjectured (based on some academic work done by others) that people born in the early months of the year would be overrepresented on World Cup rosters. The underlying theory is that in 1997, FIFA made January 1 the cutoff for determining ages in all international soccer competitions. If this rule had an important impact in determining who made the national youth soccer teams, then these early selection rules would play out to more long run success at the highest levels of soccer. The academic evidence is that these national teams are overwhelmingly made up of players born early in the calendar year, even on the age 21 and under teams, where a few months of physical development isn’t likely to make a big difference. A commenter on our blog, Bill Loyd, has done some hard work to gather data and argues that for past World Cups and for a few of the 2006 squads that he found, he doesn’t see the pattern we predict.

Why might this be the case? For the earlier World Cups, it might not be very surprising that no pattern is there because the FIFA rule didn’t come in until 1997. More fundamentally, the FIFA selection rules and the rules that different countries use for play within the county differ.

For instance, as many readers have emailed us, in the U.S., the age cutoffs tend to be in the summer. In Germany, the within country age cutoff is August 1. Thus, in soccer there are two different competitive pressures at work: one pushing towards more players born in the early months and the other towards more players in the later months. Much of the study of birth-date timing focuses on the cutoff rules within countries, virtually all of them finding important effects.

In light of this difference between FIFA and country rules, the example we gave of the World Cup might not have been the best one, even though the age effect is very strong in the national youth squads that feed many World Cup teams.

This shouldn’t distract from the important fact that the evidence in the literature overwhelming supports the basic point — that across many activities, you can identify long-term effects of essentially arbitrary age cutoffs early in life.

Perhaps a better example than the World Cup would have been the N.H.L. Here is one graph that I found on the web of the birth month of NHL hockey players versus Canadians and Americans more generally:

The black-and-white dots are the NHL players, who are much more likely to be born in January and February and much less likely to be born September-December. This is the sort of pattern that appears over and over in these sorts of studies.

Some other readers have offered a clever, very Freakonomics-y alternative explanation for these age patterns: the parents are lying about their child’s birthday. If the parents want the kid to be a star, they take an older kid and change his date of birth to make him eligible to play with younger children. While I don’t think this is actually the primary reason for what people find in these studies, is definitely worth thinking about.

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COMMENTS: 118


  1. Mae says:

    This is a general comment about another freak-o change to a formerly exclusive and greedy “profession.”

    The article:
    http://www.nytimes.com/2006/05/11/garden/11trade.html
    Title: “The Secret Source is Out”

    This article documents that the web and other pressures are changing the privileges of interior decorators. They used to get outrageous commissions partly because they had sources of products open only to “the trade.” Now more and more such sources are capitulating to pressure to sell to any buyer. Sound like realtors? Sound like travel?

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  2. Mae says:

    This is a general comment about another freak-o change to a formerly exclusive and greedy “profession.”

    The article:
    http://www.nytimes.com/2006/05/11/garden/11trade.html
    Title: “The Secret Source is Out”

    This article documents that the web and other pressures are changing the privileges of interior decorators. They used to get outrageous commissions partly because they had sources of products open only to “the trade.” Now more and more such sources are capitulating to pressure to sell to any buyer. Sound like realtors? Sound like travel?

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  3. rsaunders says:

    I used to see the same age effect as a swim coach. For our summer club, the age cutoff was June 1; so, calendar-age 15 year-olds competing against 13-14 year-olds, and they tended to fare substantially better.

    However, I’m curious why you didn’t consider the more obvious age-cutoff example: school enrollment? As an October birthday, besides being among the last to drive, I also always thought I was among the least socially adept, whereas my Nov and Dec birthday friends, who were one-grade below me in school, seemed to fare better. Of course, I could be fishing for an excuse for myself, but…

    Also, I’ve always thought that similar age cutoffs happen with childbirth, that you should use gestational age (assuming you can accuratley measure the conception date) rather than calendar age for lots of early childhood milestones, that it is better (for the child) to be in utero for 40 weeks than 36 weeks, except to the degree that endangering the mother’s help endanger’s the child’s. For many milestones, it probably doesn’t matter too much because they get the same exposures out of the womb, but I would think that the extra time would in some way better position the child physically/developmentally to handle what they’re exposed to.

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  4. rsaunders says:

    I used to see the same age effect as a swim coach. For our summer club, the age cutoff was June 1; so, calendar-age 15 year-olds competing against 13-14 year-olds, and they tended to fare substantially better.

    However, I’m curious why you didn’t consider the more obvious age-cutoff example: school enrollment? As an October birthday, besides being among the last to drive, I also always thought I was among the least socially adept, whereas my Nov and Dec birthday friends, who were one-grade below me in school, seemed to fare better. Of course, I could be fishing for an excuse for myself, but…

    Also, I’ve always thought that similar age cutoffs happen with childbirth, that you should use gestational age (assuming you can accuratley measure the conception date) rather than calendar age for lots of early childhood milestones, that it is better (for the child) to be in utero for 40 weeks than 36 weeks, except to the degree that endangering the mother’s help endanger’s the child’s. For many milestones, it probably doesn’t matter too much because they get the same exposures out of the womb, but I would think that the extra time would in some way better position the child physically/developmentally to handle what they’re exposed to.

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  5. Andi says:

    rsaunders, The papers Levitt and Dubner link to do show that a late month born child is more likely to be identified as “learning disabled,” be retained, etc.
    I’m only guessing the authors chose the more sexy sports data over the most disconcerting, depressing, or alarmist data for their article.

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  6. Andi says:

    rsaunders, The papers Levitt and Dubner link to do show that a late month born child is more likely to be identified as “learning disabled,” be retained, etc.
    I’m only guessing the authors chose the more sexy sports data over the most disconcerting, depressing, or alarmist data for their article.

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  7. JCB says:

    Seems to work for baseball too.
    Link

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  8. JCB says:

    Seems to work for baseball too.
    Link

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  9. dkane says:

    “one graph that I found on the web” is an, uh, interesting piece of evidence. Amazing what appears on the web. Why not provide a link so that Bill Lloyd can check if this claim is as, uh, accurate as the previous claims made about World Cup soccer players?

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  10. dkane says:

    “one graph that I found on the web” is an, uh, interesting piece of evidence. Amazing what appears on the web. Why not provide a link so that Bill Lloyd can check if this claim is as, uh, accurate as the previous claims made about World Cup soccer players?

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  11. A reader writes:

    Gentlemen,

    I am a hockey broadcaster in Canada who thoroughly enjoyed “Freakonomics”.
    I read with interest the piece in the NY Times magazine about European
    soccer stars and their birth months (“A Star Is Made”, May 7).

    Hockey provides an interesting case study. Most elite hockey players from
    North America are born in the first three months of the year. In fact,
    approximately 3/4 of the players in the Hockey Hall of Fame were born in
    January, February or March.

    But it’s an entirely different case among elite level European players,
    especially those from the old Eastern Bloc. Why? Because unlike North
    America, hockey programs in those nations are part of the school system, and
    thus use the school calendar as their basis. When looking at the highest
    scoring European players, we find mostly September, October and November
    birthdates.

    The “birth month” issue is well known in Canadian hockey circles, as
    evidenced by an episode in suburban Toronto several years ago. A couple had
    a child born on New Year’s eve, very close to midnight. The father begged
    the doctor to alter the birth records to say that the child was born on
    January 1.

    The doctor suspected that the father may have been trying to pull a “New
    Year’s baby” scam and refused. The discussion became heated, and the police
    were brought in.

    It turns out the father was an obsessed hockey parent who wanted to give his
    son “a leg up” in his future hockey endeavors by having his child be the
    oldest in his age group as opposed to the youngest.

    Your work is entertaining and excellent. Please keep it up.

    Sincerely,

    Gord Miller
    Commentator
    The Sports Network

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  12. A reader writes:

    Gentlemen,

    I am a hockey broadcaster in Canada who thoroughly enjoyed “Freakonomics”.
    I read with interest the piece in the NY Times magazine about European
    soccer stars and their birth months (“A Star Is Made”, May 7).

    Hockey provides an interesting case study. Most elite hockey players from
    North America are born in the first three months of the year. In fact,
    approximately 3/4 of the players in the Hockey Hall of Fame were born in
    January, February or March.

    But it’s an entirely different case among elite level European players,
    especially those from the old Eastern Bloc. Why? Because unlike North
    America, hockey programs in those nations are part of the school system, and
    thus use the school calendar as their basis. When looking at the highest
    scoring European players, we find mostly September, October and November
    birthdates.

    The “birth month” issue is well known in Canadian hockey circles, as
    evidenced by an episode in suburban Toronto several years ago. A couple had
    a child born on New Year’s eve, very close to midnight. The father begged
    the doctor to alter the birth records to say that the child was born on
    January 1.

    The doctor suspected that the father may have been trying to pull a “New
    Year’s baby” scam and refused. The discussion became heated, and the police
    were brought in.

    It turns out the father was an obsessed hockey parent who wanted to give his
    son “a leg up” in his future hockey endeavors by having his child be the
    oldest in his age group as opposed to the youngest.

    Your work is entertaining and excellent. Please keep it up.

    Sincerely,

    Gord Miller
    Commentator
    The Sports Network

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  13. To dkane:

    I don’t know where Levitt’s graph comes from, but here’s a link we’ve cited a few times in related threads here that should be of interest to you:

    http://www.socialproblemindex.ualberta.ca/relage.htm

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  14. To dkane:

    I don’t know where Levitt’s graph comes from, but here’s a link we’ve cited a few times in related threads here that should be of interest to you:

    http://www.socialproblemindex.ualberta.ca/relage.htm

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  15. dratskee says:

    I’m glad you guys posted this correction/follow-up! Interesting topic. I skipped a grade and have a late birthday, so I’m pleased to have an excuse for my poor athletic skills.

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  16. dratskee says:

    I’m glad you guys posted this correction/follow-up! Interesting topic. I skipped a grade and have a late birthday, so I’m pleased to have an excuse for my poor athletic skills.

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  17. David Kane says:

    Mr. Dubner,

    Thanks for taking the time to provide that link. No doubt I am an idiot, but after looking at the site for 15 minutes, I could not find a single piece of data that supported the factual claim that — at the adult, elite level (i.e., World Cup soccer, NHL hockey) — there is an month-of-birth effect. (Everyone seems to agree that there is such an effect under age 20 or so.)

    Could you specify the precise location at that site with such data?

    Thanks for your time.

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  18. David Kane says:

    Mr. Dubner,

    Thanks for taking the time to provide that link. No doubt I am an idiot, but after looking at the site for 15 minutes, I could not find a single piece of data that supported the factual claim that — at the adult, elite level (i.e., World Cup soccer, NHL hockey) — there is an month-of-birth effect. (Everyone seems to agree that there is such an effect under age 20 or so.)

    Could you specify the precise location at that site with such data?

    Thanks for your time.

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  19. Bill L. Lloyd says:

    Mr. Levitt,

    Thank you for posting on my World Cup findings.

    I’m afraid I still don’t see any good evidence for your and Mr. Dubner’s thesis.

    Not trusting a graph that you “found on the web,” with no citation, I tallied up a sample of 158 NHL players.

    At random, I chose five awards: the Frank J. Selke Award for Best Defensive Forward; Rookie of the Year; Playoffs MVP; the Lady Byng Trophy; and the Masterton Sportsmanship Award. I figured, if there’s a way to calculate who “elite” hockey players are, award-winners is the most accurate criterion.

    I counted all 158 players who had won one or more of these awards, being sure not to count people who had won two or more of them (or the same one twice), which is easy to do, since my browser highlights the links I’ve visited already.

    Results: of the 158 players, 79 were born in the first six months of the year, 79 were born in the last six months. An exact tie (oddly enough, I also found exact ties in the 1982 and 1986 World Cups).

    Here are the Wikipedia pages:

    http://en.wikipedia.org/wiki/Bill_Masterton_Memorial_Trophy

    http://en.wikipedia.org/wiki/Calder_Memorial_Trophy

    http://en.wikipedia.org/wiki/Conn_Smythe_Trophy

    http://en.wikipedia.org/wiki/Lady_Byng_Memorial_Trophy

    http://en.wikipedia.org/wiki/Frank_J._Selke_Trophy

    The monthly breakdowns reveal no pattern that I can discern:

    Jan 12
    Feb 12
    Mar 18
    Apr 13
    May 12
    Jun 12
    Jul 19
    Aug 10
    Sept 8
    Oct 15
    Nov 10
    Dec 17

    I find it surprising that a high-level economist relies on “one graph that [he] found on the web” as the keystone of a New York Times article.

    Perhaps badminton, Mr. Levitt? Shall I check?

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  20. Bill L. Lloyd says:

    Mr. Levitt,

    Thank you for posting on my World Cup findings.

    I’m afraid I still don’t see any good evidence for your and Mr. Dubner’s thesis.

    Not trusting a graph that you “found on the web,” with no citation, I tallied up a sample of 158 NHL players.

    At random, I chose five awards: the Frank J. Selke Award for Best Defensive Forward; Rookie of the Year; Playoffs MVP; the Lady Byng Trophy; and the Masterton Sportsmanship Award. I figured, if there’s a way to calculate who “elite” hockey players are, award-winners is the most accurate criterion.

    I counted all 158 players who had won one or more of these awards, being sure not to count people who had won two or more of them (or the same one twice), which is easy to do, since my browser highlights the links I’ve visited already.

    Results: of the 158 players, 79 were born in the first six months of the year, 79 were born in the last six months. An exact tie (oddly enough, I also found exact ties in the 1982 and 1986 World Cups).

    Here are the Wikipedia pages:

    http://en.wikipedia.org/wiki/Bill_Masterton_Memorial_Trophy

    http://en.wikipedia.org/wiki/Calder_Memorial_Trophy

    http://en.wikipedia.org/wiki/Conn_Smythe_Trophy

    http://en.wikipedia.org/wiki/Lady_Byng_Memorial_Trophy

    http://en.wikipedia.org/wiki/Frank_J._Selke_Trophy

    The monthly breakdowns reveal no pattern that I can discern:

    Jan 12
    Feb 12
    Mar 18
    Apr 13
    May 12
    Jun 12
    Jul 19
    Aug 10
    Sept 8
    Oct 15
    Nov 10
    Dec 17

    I find it surprising that a high-level economist relies on “one graph that [he] found on the web” as the keystone of a New York Times article.

    Perhaps badminton, Mr. Levitt? Shall I check?

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  21. David Kane says:

    It appears that Dr. Levitt found his graph here.

    Reliable data? Tough to know. Wonder why Dr. Levitt didn’t follow the universal blogospheric practice of providing the link? You’ll have to ask him. But I certainly wouldn’t put an excessive amount of faith in a webpage that starts with this:

    Do the world’s best hockey players have a common cosmic signature? Does Mercury tend to be in a certain area of the sky when a professional hockey player is born? I am intrigued by that question and many, many others and what follows are the observations I have made during the course of the project. Stay with me, this gets very interesting.

    During the 2001-2002 hockey season the National Hockey League was composed of 30 professional teams located in Canada and the United States of America, averaging 26 players per team (range 22 to 31), a total of 761 individuals. Birth information was gathered for each player including the day, month, year, city and country of birth. The time of each player’s birth was not readily available and so the time for each player was set for noon on the day of birth, halfway through the planetary motions for the day. The birth information was input to Matrix Software’s Win*Star Plus program which accurately produced a heliogram for each player.

    HELIOGRAMS

    A heliogram is a two dimensional arrangement of the planets around the Sun at the time of the birth of any individual. The position in the heliogram of Mercury, Venus, Earth and Mars for each player was transferred into Microsoft’s Access database along with information about the heliogram “type” and the planetary patterns associated with the heliogram. The heliogram is a heliocentric view of our solar system and includes the positions of all the planets which orbit our sun including Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The heliogram is divided into 12 equal sized sectors each of 30° and labeled sectors 1, 2, 3 etc. in a clockwise direction from the East. Each planet in a heliogram has a planetary address; for example, a planetary address of 1215 means that the planet is in sector 12 at the 15th degree.

    Good to know. Perhaps the next New York Times article will discuss the freakonomics of heliograms. I look forward to it.

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  22. David Kane says:

    It appears that Dr. Levitt found his graph here.

    Reliable data? Tough to know. Wonder why Dr. Levitt didn’t follow the universal blogospheric practice of providing the link? You’ll have to ask him. But I certainly wouldn’t put an excessive amount of faith in a webpage that starts with this:

    Do the world’s best hockey players have a common cosmic signature? Does Mercury tend to be in a certain area of the sky when a professional hockey player is born? I am intrigued by that question and many, many others and what follows are the observations I have made during the course of the project. Stay with me, this gets very interesting.

    During the 2001-2002 hockey season the National Hockey League was composed of 30 professional teams located in Canada and the United States of America, averaging 26 players per team (range 22 to 31), a total of 761 individuals. Birth information was gathered for each player including the day, month, year, city and country of birth. The time of each player’s birth was not readily available and so the time for each player was set for noon on the day of birth, halfway through the planetary motions for the day. The birth information was input to Matrix Software’s Win*Star Plus program which accurately produced a heliogram for each player.

    HELIOGRAMS

    A heliogram is a two dimensional arrangement of the planets around the Sun at the time of the birth of any individual. The position in the heliogram of Mercury, Venus, Earth and Mars for each player was transferred into Microsoft’s Access database along with information about the heliogram “type” and the planetary patterns associated with the heliogram. The heliogram is a heliocentric view of our solar system and includes the positions of all the planets which orbit our sun including Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The heliogram is divided into 12 equal sized sectors each of 30? and labeled sectors 1, 2, 3 etc. in a clockwise direction from the East. Each planet in a heliogram has a planetary address; for example, a planetary address of 1215 means that the planet is in sector 12 at the 15th degree.

    Good to know. Perhaps the next New York Times article will discuss the freakonomics of heliograms. I look forward to it.

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  23. SteveSailer says:

    Dear Dr. Levitt:

    Thanks for looking into this further.

    Congratulations to Bill L. Lloyd for his hard work and insights.

    This kind of information could help answer questions about the relative importance of nature vs. nurture in different sports. For example, I would hypothesize that age cutoffs and birthdates would have little correlation with who makes the NBA (especially at center and forward), since height, which is highly heritable, is so overwhelmingly important and thus most players are drawn from the right edge of the height bell curve. If you are Manute Bol, the 7′-7″ Dinka tribesman from the Sudan, you can enjoy a lengthy (if curious) career in the NBA, and lead the league in blocked shots, even though you didn’t see a basketball in your life until you are 19.

    On the other hand, perhaps a sport like soccer where players mostly are fairly average in size is more driven by nurture than nature than is basketball. It’s hard to imagine the soccer equivalent of Manute Bol or of Nigerian Hall of Fame basketball center Hakeem Olajuwon, a seven foot who switched from being soccer goalie to a basketball player at about 16.

    I don’t pretend to know enough about soccer to make a prediction, but the relatively slow progress of the U.S. in the soccer World Cup, compared to say, Argentina in Olympic basketball, might suggest that culture is a bigger driver of success in soccer than in basketball.

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  24. SteveSailer says:

    Dear Dr. Levitt:

    Thanks for looking into this further.

    Congratulations to Bill L. Lloyd for his hard work and insights.

    This kind of information could help answer questions about the relative importance of nature vs. nurture in different sports. For example, I would hypothesize that age cutoffs and birthdates would have little correlation with who makes the NBA (especially at center and forward), since height, which is highly heritable, is so overwhelmingly important and thus most players are drawn from the right edge of the height bell curve. If you are Manute Bol, the 7′-7″ Dinka tribesman from the Sudan, you can enjoy a lengthy (if curious) career in the NBA, and lead the league in blocked shots, even though you didn’t see a basketball in your life until you are 19.

    On the other hand, perhaps a sport like soccer where players mostly are fairly average in size is more driven by nurture than nature than is basketball. It’s hard to imagine the soccer equivalent of Manute Bol or of Nigerian Hall of Fame basketball center Hakeem Olajuwon, a seven foot who switched from being soccer goalie to a basketball player at about 16.

    I don’t pretend to know enough about soccer to make a prediction, but the relatively slow progress of the U.S. in the soccer World Cup, compared to say, Argentina in Olympic basketball, might suggest that culture is a bigger driver of success in soccer than in basketball.

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  25. SteveSailer says:

    On the other hand, the rapid decline of the USA Olympic basketball team since the awesome 1992 Dream Team may be an example of negative cultural influence on basketball success at the _team_ level.

    The NBA stars who failed so ignominously at the 2004 Athens Olympics all grew up since the emergence of gangsta rap during the early years of the crack wars in the late 1980s. (NWA’s “Straight Outta Compton” album was the first hit gangsta rap album in 1988.) Perhaps many contemporary NBA stars have internalized a lot of the chest-beating machismo celebrated in gangsta rap, which might help explain why they played as a team so much worse than the Dream Team of 1992, who were all full grown by the time gangsta rap arrived.

    Obviously, this is speculative, but the timing is at least suggestive.

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  26. SteveSailer says:

    On the other hand, the rapid decline of the USA Olympic basketball team since the awesome 1992 Dream Team may be an example of negative cultural influence on basketball success at the _team_ level.

    The NBA stars who failed so ignominously at the 2004 Athens Olympics all grew up since the emergence of gangsta rap during the early years of the crack wars in the late 1980s. (NWA’s “Straight Outta Compton” album was the first hit gangsta rap album in 1988.) Perhaps many contemporary NBA stars have internalized a lot of the chest-beating machismo celebrated in gangsta rap, which might help explain why they played as a team so much worse than the Dream Team of 1992, who were all full grown by the time gangsta rap arrived.

    Obviously, this is speculative, but the timing is at least suggestive.

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  27. In post No. 9 above, David Kane wrote:

    No doubt I am an idiot, but after looking at the site for 15 minutes, I could not find a single piece of data that supported the factual claim that—- at the adult, elite level (i.e., World Cup soccer, NHL hockey)—- there is an month-of-birth effect.

    The site I had referred him to, upon his request for further data about relative-age effect in the N.H.L., was this one:

    http://www.socialproblemindex.ualberta.ca/relage.htm

    I don’t necessarily agree with David that he is an idiot, but the N.H.L. mention is right there under the site’s first section, titled “Month of Birth and Elite Hockey,” whose text reads, in part, as follows:

    The Figure at left shows the distribution of birth-months of players in two Canadian major junior hockey leagues (the Ontario Junior Hockey League and the Western Hockey League). The data indicate that the probability of success in high calibre hockey is dramatically reduced for those born at the end of the year. Furthermore, among National League Hockey Players who were active in the early 1980s, about 40% were born in the first quarter of the year, 30% in the second, 20% in the third, and less than 10% were born in the final quarter.

    In terms of playing at a high level, boys born in the last part of the year have a much lower chance than those born at the beginning of the year. The fact that January and December, which are juxtaposed, show such dissimilar results, suggests that it is not the weather during conception or birth that has made the difference.

    Source: Barnsley RH, Thompson AH, Barnsley PE (1985). Hockey success and birth-date: The relative age effect. Journal of the Canadian Association for Health, Physical Education, and Recreation, Nov.-Dec., 23-28.

    You could also look at another document posted on this site:

    http://www.freakonomics.com/pdf/RelativeAgeEffectSportsMusch2001.pdf

    Go to Table 1, p. 150, or just search for “ice hockey.”

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  28. In post No. 9 above, David Kane wrote:

    No doubt I am an idiot, but after looking at the site for 15 minutes, I could not find a single piece of data that supported the factual claim that– at the adult, elite level (i.e., World Cup soccer, NHL hockey)– there is an month-of-birth effect.

    The site I had referred him to, upon his request for further data about relative-age effect in the N.H.L., was this one:

    http://www.socialproblemindex.ualberta.ca/relage.htm

    I don’t necessarily agree with David that he is an idiot, but the N.H.L. mention is right there under the site’s first section, titled “Month of Birth and Elite Hockey,” whose text reads, in part, as follows:

    The Figure at left shows the distribution of birth-months of players in two Canadian major junior hockey leagues (the Ontario Junior Hockey League and the Western Hockey League). The data indicate that the probability of success in high calibre hockey is dramatically reduced for those born at the end of the year. Furthermore, among National League Hockey Players who were active in the early 1980s, about 40% were born in the first quarter of the year, 30% in the second, 20% in the third, and less than 10% were born in the final quarter.

    In terms of playing at a high level, boys born in the last part of the year have a much lower chance than those born at the beginning of the year. The fact that January and December, which are juxtaposed, show such dissimilar results, suggests that it is not the weather during conception or birth that has made the difference.

    Source: Barnsley RH, Thompson AH, Barnsley PE (1985). Hockey success and birth-date: The relative age effect. Journal of the Canadian Association for Health, Physical Education, and Recreation, Nov.-Dec., 23-28.

    You could also look at another document posted on this site:

    http://www.freakonomics.com/pdf/RelativeAgeEffectSportsMusch2001.pdf

    Go to Table 1, p. 150, or just search for “ice hockey.”

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  29. Bill L. Lloyd says:

    Mr. Levitt writes:

    “If this rule had an important impact in determining who made the national youth soccer teams, then these early selection rules would play out to more long run success at the highest levels of soccer [at the pro level, this has not been proven at all; it's sheer conjecture on Levitt's part, both cause and effect]. The academic evidence is that these national teams are overwhelmingly made up of players born early in the calendar year, even on the age 21 and under teams, where a few months of physical development isn’t likely to make a big difference.”

    For about the tenth time, *no one here is disputing whether national youth teams are more likely to feature players with early year births”. This is universally agreed upon. What is being disputed is whether this effect lasts in adult pro leagues.*

    Mr. Levitt has not provided a citation for his hockey graph that he “found on the web,” so we cannot check it. I hope he didn’t get it from the site Mr. Kane found it at — some kind of astrology site — but we’ll wait for a citation from Mr. Levitt on that.

    This isn’t some hard-to-replicate laboratory study. It’s counting birthdays of hockey and soccer players on Wikipedia.

    We still have no good evidence that birth month has any effect on pro team makeup in hockey or soccer. If there is such evidence, I’d be glad to take a look at it.

    Keep in mind that, on most topics, you can find a study that says A and a study that says the opposite of A. You can also find studies for anything in between.

    That’s why I like to use my own eyes when it’s feasible, and remain skeptical of theories that don’t sound right.

    It just doesn’t sound plausible to me that Mr. Levitt and Mr. Dubner’s thesis is correct. January kids growing up might be borderline talented and slide onto all-star teams through adolescence boosted by their several-month advantage, but that effect would likely dissipate greatly in the post-adolescence college years, and then disappear by the time they’re pros.

    If the evidence shows otherwise, I’ll look at Mr. Levitt and Dubner’s explanations for the phenomenon.

    But so far, the evidence doesn’t show that there is any phenomenon.

    It makes more sense to me that later-year kids would get lots of good practice growing up fighting against slightly bigger kids. This might offset (or more than offset) the self-esteem and extra coaching early-year borderline all-star kids would get.

    Anyway, like I said on the previous thread: before going into complex reasons how the moon came to be made of green cheese, let’s first determine whether it actually is made of green cheese.

    Doesn’t look like it from here, Mr. Levitt.

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  30. Bill L. Lloyd says:

    Mr. Levitt writes:

    “If this rule had an important impact in determining who made the national youth soccer teams, then these early selection rules would play out to more long run success at the highest levels of soccer [at the pro level, this has not been proven at all; it's sheer conjecture on Levitt's part, both cause and effect]. The academic evidence is that these national teams are overwhelmingly made up of players born early in the calendar year, even on the age 21 and under teams, where a few months of physical development isn’t likely to make a big difference.”

    For about the tenth time, *no one here is disputing whether national youth teams are more likely to feature players with early year births”. This is universally agreed upon. What is being disputed is whether this effect lasts in adult pro leagues.*

    Mr. Levitt has not provided a citation for his hockey graph that he “found on the web,” so we cannot check it. I hope he didn’t get it from the site Mr. Kane found it at — some kind of astrology site — but we’ll wait for a citation from Mr. Levitt on that.

    This isn’t some hard-to-replicate laboratory study. It’s counting birthdays of hockey and soccer players on Wikipedia.

    We still have no good evidence that birth month has any effect on pro team makeup in hockey or soccer. If there is such evidence, I’d be glad to take a look at it.

    Keep in mind that, on most topics, you can find a study that says A and a study that says the opposite of A. You can also find studies for anything in between.

    That’s why I like to use my own eyes when it’s feasible, and remain skeptical of theories that don’t sound right.

    It just doesn’t sound plausible to me that Mr. Levitt and Mr. Dubner’s thesis is correct. January kids growing up might be borderline talented and slide onto all-star teams through adolescence boosted by their several-month advantage, but that effect would likely dissipate greatly in the post-adolescence college years, and then disappear by the time they’re pros.

    If the evidence shows otherwise, I’ll look at Mr. Levitt and Dubner’s explanations for the phenomenon.

    But so far, the evidence doesn’t show that there is any phenomenon.

    It makes more sense to me that later-year kids would get lots of good practice growing up fighting against slightly bigger kids. This might offset (or more than offset) the self-esteem and extra coaching early-year borderline all-star kids would get.

    Anyway, like I said on the previous thread: before going into complex reasons how the moon came to be made of green cheese, let’s first determine whether it actually is made of green cheese.

    Doesn’t look like it from here, Mr. Levitt.

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  31. David Kane says:

    Apologies for posting so many items in a row, but this is just too fun.

    Although I can not vouch for the accuracy of this data, the Sportsnet.ca site seems to provide a reasonable set of data on the 971 players in the NHL for 2005-2006. (I confess that it is not an astrology site, like the one used by Dr. Levitt, but please humor me.)

    Now, if there are 971 players and 12 months in the year, how would we expect the birth-months to be distributed (ignoring days in the month, leap years and other details)? The null hypothesis would be 81 or so per month.

    I had to play around with the options (use Sub-sort after checking Birth Month under personal info) and I could not figure out a way to provide a link to the results. But, by my quick count, here are the number of players born per month at the start and end of the year.

    January 97
    February 105
    March 86

    October 66
    November 52
    December 64

    Pretty impressive for the Freakonomics claim! Here are the results by quarter of the year.

    Jan-Mar 286
    Apr-Jun 278
    Jul-Sep 221
    Oct-Dec 180

    Note that the month values do not add up exactly to the quarterly sums. The interface is somewhat hard to use and I could easily be making a mistake.

    Note also that I have ignored issues of country of birth (what should really be country-of-junior-hockey-playing). I also ignore the monthly birth rates for a matched population. (If more people are born in the first quarter of the year than the last quarter, we would expect to see the same being true for hockey players.)

    In any event, I would conclude that there is evidence that current NHL hockey players are more likely to be born earlier in the year than later. I will leave significance tests for someone smarter than I to do.

    Could this be due to cut-off dates for junior hockey? Perhaps. Key test might be to see if this pattern holds for different countries with other cut-off dates.

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  32. David Kane says:

    Apologies for posting so many items in a row, but this is just too fun.

    Although I can not vouch for the accuracy of this data, the Sportsnet.ca site seems to provide a reasonable set of data on the 971 players in the NHL for 2005-2006. (I confess that it is not an astrology site, like the one used by Dr. Levitt, but please humor me.)

    Now, if there are 971 players and 12 months in the year, how would we expect the birth-months to be distributed (ignoring days in the month, leap years and other details)? The null hypothesis would be 81 or so per month.

    I had to play around with the options (use Sub-sort after checking Birth Month under personal info) and I could not figure out a way to provide a link to the results. But, by my quick count, here are the number of players born per month at the start and end of the year.

    January 97
    February 105
    March 86

    October 66
    November 52
    December 64

    Pretty impressive for the Freakonomics claim! Here are the results by quarter of the year.

    Jan-Mar 286
    Apr-Jun 278
    Jul-Sep 221
    Oct-Dec 180

    Note that the month values do not add up exactly to the quarterly sums. The interface is somewhat hard to use and I could easily be making a mistake.

    Note also that I have ignored issues of country of birth (what should really be country-of-junior-hockey-playing). I also ignore the monthly birth rates for a matched population. (If more people are born in the first quarter of the year than the last quarter, we would expect to see the same being true for hockey players.)

    In any event, I would conclude that there is evidence that current NHL hockey players are more likely to be born earlier in the year than later. I will leave significance tests for someone smarter than I to do.

    Could this be due to cut-off dates for junior hockey? Perhaps. Key test might be to see if this pattern holds for different countries with other cut-off dates.

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  33. Bill L. Lloyd says:

    Mr. Dubner writes:

    “The Figure at left shows the distribution of birth-months of players in two Canadian major junior hockey leagues (the Ontario Junior Hockey League and the Western Hockey League). The data indicate that the probability of success in high calibre hockey is dramatically reduced for those born at the end of the year.”

    As we have already well-established on these threads, Mr. Dubner, *no one is questioning whether youth leagues of any sport have higher percentages of early-year births. Everyone on these threads agrees with that. We are only disputing whether this effect carries through into adulthood.*

    Dubner, citing the study:

    “Furthermore, among National League Hockey Players who were active in the early 1980s, about 40% were born in the first quarter of the year, 30% in the second, 20% in the third, and less than 10% were born in the final quarter.”

    I think that the “National League Hockey” cited in this study is not the NHL, but this Canadian junior governing body:

    http://en.wikipedia.org/wiki/Canadian_Hockey_League

    As the Wikipedia page shows, this league is for players aged 15-20 only.

    Mr. Dubner, did you really think that 70% of NHL players were born in the first six months of the year? That stat alone would’ve set off my bullcrap meter bigtime.

    Indeed, I just surveyed 158 NHL greats (see upthread) and came up with 79 born in the first six months of the year, 79 born in the last six months.

    So we are back where we started with Levitt and Dubner. Their soccer data didn’t hold up, and now their hockey data is, frankly, embarrassing.

    Another sport you’d care to try, guys? Sorry to be snotty, but this is amateur hour economics and social science.

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  34. Bill L. Lloyd says:

    Mr. Dubner writes:

    “The Figure at left shows the distribution of birth-months of players in two Canadian major junior hockey leagues (the Ontario Junior Hockey League and the Western Hockey League). The data indicate that the probability of success in high calibre hockey is dramatically reduced for those born at the end of the year.”

    As we have already well-established on these threads, Mr. Dubner, *no one is questioning whether youth leagues of any sport have higher percentages of early-year births. Everyone on these threads agrees with that. We are only disputing whether this effect carries through into adulthood.*

    Dubner, citing the study:

    “Furthermore, among National League Hockey Players who were active in the early 1980s, about 40% were born in the first quarter of the year, 30% in the second, 20% in the third, and less than 10% were born in the final quarter.”

    I think that the “National League Hockey” cited in this study is not the NHL, but this Canadian junior governing body:

    http://en.wikipedia.org/wiki/Canadian_Hockey_League

    As the Wikipedia page shows, this league is for players aged 15-20 only.

    Mr. Dubner, did you really think that 70% of NHL players were born in the first six months of the year? That stat alone would’ve set off my bullcrap meter bigtime.

    Indeed, I just surveyed 158 NHL greats (see upthread) and came up with 79 born in the first six months of the year, 79 born in the last six months.

    So we are back where we started with Levitt and Dubner. Their soccer data didn’t hold up, and now their hockey data is, frankly, embarrassing.

    Another sport you’d care to try, guys? Sorry to be snotty, but this is amateur hour economics and social science.

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  35. Bill Lloyd,

    Sorry, my mistake re my post 13 and your post 16. Thanks for correction. I’m pretty sure I have my leagues straight in the other cite, however:

    http://www.freakonomics.com/pdf/RelativeAgeEffectSportsMusch2001.pdf

    (Table 1, p. 150.)

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  36. Bill Lloyd,

    Sorry, my mistake re my post 13 and your post 16. Thanks for correction. I’m pretty sure I have my leagues straight in the other cite, however:

    http://www.freakonomics.com/pdf/RelativeAgeEffectSportsMusch2001.pdf

    (Table 1, p. 150.)

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  37. Bill L. Lloyd says:

    David Kane,

    Great work — that site provides a 59%-41% split in 2005-06 NHL players. So this effect does exist in pro hockey.

    I wonder if it’s a new effect, given that my 158-player sample, which spanned many decades, found a 50-50 split.

    Also, I apologize to Mr. Levitt and Mr. Dubner for my “amateur hour” comment. That was unnecessarily snotty.

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  38. Bill L. Lloyd says:

    David Kane,

    Great work — that site provides a 59%-41% split in 2005-06 NHL players. So this effect does exist in pro hockey.

    I wonder if it’s a new effect, given that my 158-player sample, which spanned many decades, found a 50-50 split.

    Also, I apologize to Mr. Levitt and Mr. Dubner for my “amateur hour” comment. That was unnecessarily snotty.

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  39. SteveSailer says:

    Dear Mr. Kane:

    Thanks. I wonder if this NHL data could turn out to be evidence for the kind of market inefficiencies that were identified by Bill James in the baseball business from 1975 onward, and have recently been exploited by Billy Beane and others in the big leagues — e.g., for decades, good-looking athletes who swung at too many bad pitches were favored by scouts over less athletic hitters who got more walks because of their eagle eye for bad pitches.

    I am informed by a reader that the NHL draft of Canadian players is largely restricted to 18 year olds and is quite biased toward those born early in the year due to their better performance in national and international junior showcases.

    This drafting behavior could be an efficient response if born-early-in-the year players remain objectively better throughout their career. Or it could be a market inefficiency.

    One of Bill James’ first major finding a couple of decades ago was that in baseball draft picks out of college enjoyed better major league careers on average than draft picks out of high school.

    Perhaps hockey has a market inefficiency because there isn’t much of a Canadian college hockey culture, so you either make it at age 18 or you don’t. And thus kids who are 18 and 364 days do better in the draft than kids who are 18 and 1 day on average.

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  40. SteveSailer says:

    Dear Mr. Kane:

    Thanks. I wonder if this NHL data could turn out to be evidence for the kind of market inefficiencies that were identified by Bill James in the baseball business from 1975 onward, and have recently been exploited by Billy Beane and others in the big leagues — e.g., for decades, good-looking athletes who swung at too many bad pitches were favored by scouts over less athletic hitters who got more walks because of their eagle eye for bad pitches.

    I am informed by a reader that the NHL draft of Canadian players is largely restricted to 18 year olds and is quite biased toward those born early in the year due to their better performance in national and international junior showcases.

    This drafting behavior could be an efficient response if born-early-in-the year players remain objectively better throughout their career. Or it could be a market inefficiency.

    One of Bill James’ first major finding a couple of decades ago was that in baseball draft picks out of college enjoyed better major league careers on average than draft picks out of high school.

    Perhaps hockey has a market inefficiency because there isn’t much of a Canadian college hockey culture, so you either make it at age 18 or you don’t. And thus kids who are 18 and 364 days do better in the draft than kids who are 18 and 1 day on average.

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  41. DissidentMan says:

    The official NHL website has the birthdates of all current NHL players. Someone with energy to spare might want to figure out the frequencies and determine they conform with the birth-date effect theory.

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  42. DissidentMan says:

    The official NHL website has the birthdates of all current NHL players. Someone with energy to spare might want to figure out the frequencies and determine they conform with the birth-date effect theory.

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  43. Bill L. Lloyd says:

    Steve Sailer,

    Your Canada theory sounded plausible to me, but the data doesn’t back it up. Of the 519 players in the NHL, 53.1% (!) are Canadian, and they break down 307 born Jan.-June and 212 born July-Dec., or 59%-41%. The league overall breaks down 59%-41%, so Canadian players are not exceptional in this sense.

    So maybe Levitt and Dubner are correct in their thesis, at least as regards to pro hockey. Are their other possible explanations? Why would different sports have different rates?

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  44. Bill L. Lloyd says:

    Steve Sailer,

    Your Canada theory sounded plausible to me, but the data doesn’t back it up. Of the 519 players in the NHL, 53.1% (!) are Canadian, and they break down 307 born Jan.-June and 212 born July-Dec., or 59%-41%. The league overall breaks down 59%-41%, so Canadian players are not exceptional in this sense.

    So maybe Levitt and Dubner are correct in their thesis, at least as regards to pro hockey. Are their other possible explanations? Why would different sports have different rates?

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  45. brm2000 says:

    Dear Authors:

    As to your recent NYT article on practise making
    perfect. I should point you to a small short
    philosophical treatise by Plato called the Meno. In
    the Meno Plato shows us how a slave boy with basic
    intelligence, but little education can be taught to
    reason out complicated geometry it he was shown how
    properly. The implication he (Plato) is making that
    the average person can be taught far above what their
    perception often is. It is a gem and shows that Plato
    was on to something a long time ago.

    Brm2000
    >

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  46. brm2000 says:

    Dear Authors:

    As to your recent NYT article on practise making
    perfect. I should point you to a small short
    philosophical treatise by Plato called the Meno. In
    the Meno Plato shows us how a slave boy with basic
    intelligence, but little education can be taught to
    reason out complicated geometry it he was shown how
    properly. The implication he (Plato) is making that
    the average person can be taught far above what their
    perception often is. It is a gem and shows that Plato
    was on to something a long time ago.

    Brm2000
    >

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  47. David Kane says:

    Followong DissidentMan’s suggestion, I went here for a list of 1,245 current NHL hockey players (30% more than the 971 on the Sportsnet site). As you can see, the data is not easy to work with. I saved it to text, edited out some of the html cruft and then scanned the results into R. The data is still a mess but I can search for the month strings and run an R script that produces:

    > for(i in c(“Jan”, “Feb”, “Mar”, “Apr”, “May”, “Jun”, “Jul”, “Aug”, “Sep”, “Oct”, “Nov”, “Dec”)) cat(i, “\t”, sum(x %in% c(i)), “\t”, 100*sum(x %in% c(i))/1245, “\n”)
    Jan 133 11
    Feb 125 10
    Mar 114 9.2
    Apr 119 9.6
    May 119 9.6
    Jun 123 9.9
    Jul 96 7.7
    Aug 91 7.3
    Sep 83 6.7
    Oct 84 6.7
    Nov 73 5.9
    Dec 85 6.8
    >

    First column is number of players with that birth month, second is the percentage out of 1,245.

    This is obviously a total hack, but it is consistent with Bill’s calculations. The number that jumps out, obviously, is that there are 56% more players born in January than in December.

    I may have to retract my implied criticism of Dr. Levitt’s use of that astrology site. ;-)

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  48. David Kane says:

    Followong DissidentMan’s suggestion, I went here for a list of 1,245 current NHL hockey players (30% more than the 971 on the Sportsnet site). As you can see, the data is not easy to work with. I saved it to text, edited out some of the html cruft and then scanned the results into R. The data is still a mess but I can search for the month strings and run an R script that produces:

    > for(i in c(“Jan”, “Feb”, “Mar”, “Apr”, “May”, “Jun”, “Jul”, “Aug”, “Sep”, “Oct”, “Nov”, “Dec”)) cat(i, “t”, sum(x %in% c(i)), “t”, 100*sum(x %in% c(i))/1245, “n”)
    Jan 133 11
    Feb 125 10
    Mar 114 9.2
    Apr 119 9.6
    May 119 9.6
    Jun 123 9.9
    Jul 96 7.7
    Aug 91 7.3
    Sep 83 6.7
    Oct 84 6.7
    Nov 73 5.9
    Dec 85 6.8
    >

    First column is number of players with that birth month, second is the percentage out of 1,245.

    This is obviously a total hack, but it is consistent with Bill’s calculations. The number that jumps out, obviously, is that there are 56% more players born in January than in December.

    I may have to retract my implied criticism of Dr. Levitt’s use of that astrology site. ;-)

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  49. SteveSailer says:

    A reader of my http://www.iSteve.com blog kindly sent in the following, which might explain a lot about the NHL:

    You had asked if anyone had any data on Hockey players. Well, I did some non-scientific research of Birthdays of the Top Ten drafted players from each of the last 10 drafts. And this is what I found:

    Jan 11
    Feb 14
    Mar 8
    Apr 14
    May 6
    Jun 5
    Jul 3
    Aug 7
    Sep 14
    Oct 7
    Nov 7
    Dec 4
    Sum 100

    A few pieces of trivia about Hockey players that might have some affect on who gets drafted.

    Few players get drafted after the age of 18. A few players get overlooked and then shine in college or elsewhere, but this is not often.

    You can not be drafted before the age of 18.

    Three leagues/tournaments play a huge role in who gets the most attention:

    The Canadian Major Juniors (OHL, WHL and QMJHL)

    The Under-18 Tournament (U-18)

    The World Junior Championships (WJC)

    If you do not make a major showing at one of these places, you will not be a top draft pick. The only exception would be a European/Soviet-Bloc player who plays in one of their Elite leagues but was injured for the WJC.

    I should also note that I did not factor for NHL success. That is, there are plenty of players who are drafted in the top ten who never make it in the NHL because they never mature/improve. With some more time this could be done though. Simply go to HockeyDB.com and view each draft, the site has their career stats with total number of games played. This is not that helpful for recent picks, but would be helpful for player drafted in the late 80′s early 90′s.

    Anyway, here is where I got my data: http://www.hockeydb.com/ihdb/draft/index.html (warning: lots of pop-ups)

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  50. SteveSailer says:

    A reader of my http://www.iSteve.com blog kindly sent in the following, which might explain a lot about the NHL:

    You had asked if anyone had any data on Hockey players. Well, I did some non-scientific research of Birthdays of the Top Ten drafted players from each of the last 10 drafts. And this is what I found:

    Jan 11
    Feb 14
    Mar 8
    Apr 14
    May 6
    Jun 5
    Jul 3
    Aug 7
    Sep 14
    Oct 7
    Nov 7
    Dec 4
    Sum 100

    A few pieces of trivia about Hockey players that might have some affect on who gets drafted.

    Few players get drafted after the age of 18. A few players get overlooked and then shine in college or elsewhere, but this is not often.

    You can not be drafted before the age of 18.

    Three leagues/tournaments play a huge role in who gets the most attention:

    The Canadian Major Juniors (OHL, WHL and QMJHL)

    The Under-18 Tournament (U-18)

    The World Junior Championships (WJC)

    If you do not make a major showing at one of these places, you will not be a top draft pick. The only exception would be a European/Soviet-Bloc player who plays in one of their Elite leagues but was injured for the WJC.

    I should also note that I did not factor for NHL success. That is, there are plenty of players who are drafted in the top ten who never make it in the NHL because they never mature/improve. With some more time this could be done though. Simply go to HockeyDB.com and view each draft, the site has their career stats with total number of games played. This is not that helpful for recent picks, but would be helpful for player drafted in the late 80′s early 90′s.

    Anyway, here is where I got my data: http://www.hockeydb.com/ihdb/draft/index.html (warning: lots of pop-ups)

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  51. SteveSailer says:

    So, we see a 58-42 bias for the first half of the year among the last ten years of top ten draftees of the NHL.

    So, one question would be whether this bias reflects an actual difference in long term skill, or whether it reflects a market inefficiency. For example, do NHL All-Stars reflect the same level of early-in-the-year bias?

    Another interesting perspective would be to look at American basketball and baseball players, who typically have multiple routes to the big leagues, while hockey player face this bottleneck at age 18, which gives an advantage to the 18.9 year olds versus the 18.1 year olds.

    For baseball players, the age funnel isn’t as constricting as for hockey players. They can get drafted out of high school or play in college for up to four years and get drafted out of college.

    American NBA basketball players typically were the stars of their high school teams. Although there is some national level competition (such as the McDonald’s All-Star game) for high schoolers, almost nobody with NBA potential sits on the bench in high school unless he has bad character. I believe the funnel isn’t as constricting in American basketball as in Canadian hockey. (The growth of AAU play by star teenagers has pushed American basketball somewhat in the direction of the Canadian hockey model, but I don’t know how strong that effect is.)

    Further, an enormous amount of slack is cut extremely tall youths who haven’t yet matured as basketball players. If you are 7 feet tall, you don’t have to stand out in high school to get a chance to play in college. You just have to show a moderate degree of coordination and energy and you’ll be given a chance to develop.

    High potential players can go to the NBA out of high school (although not anymore from now on), or after 1, 2, 3, or 4 years of college, or after playing in a minor league or in a less competitive overseas league.

    Now, the NBA has recently banned drafting players out of high school, even though great NBA stars like Moses Malone, Kobe Bryant, and Kevin Garnett never attended college. Many observers have argued that the decline of average years of college ball played in recent decades has caused deterioration in the knowledge of fundamental among NBA players.

    That’s because college basketball teams serve as finishing schools for raw young talents, but NBA teams are not well equipped to drill 19 year olds in basketball basics. So, in recent years a number of extremely promising basketball players who went in the NBA straight out of high school have failed to develop to their full potential because a) they aren’t taught fundamentals by pro coaches and b) they don’t get playing time.

    There are far, far more spots open on the starting line-ups of college basketball teams than pro basketball teams, so hopefully this reform will expand the bottleneck and keep it from turning into a hockey situation.

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  52. SteveSailer says:

    So, we see a 58-42 bias for the first half of the year among the last ten years of top ten draftees of the NHL.

    So, one question would be whether this bias reflects an actual difference in long term skill, or whether it reflects a market inefficiency. For example, do NHL All-Stars reflect the same level of early-in-the-year bias?

    Another interesting perspective would be to look at American basketball and baseball players, who typically have multiple routes to the big leagues, while hockey player face this bottleneck at age 18, which gives an advantage to the 18.9 year olds versus the 18.1 year olds.

    For baseball players, the age funnel isn’t as constricting as for hockey players. They can get drafted out of high school or play in college for up to four years and get drafted out of college.

    American NBA basketball players typically were the stars of their high school teams. Although there is some national level competition (such as the McDonald’s All-Star game) for high schoolers, almost nobody with NBA potential sits on the bench in high school unless he has bad character. I believe the funnel isn’t as constricting in American basketball as in Canadian hockey. (The growth of AAU play by star teenagers has pushed American basketball somewhat in the direction of the Canadian hockey model, but I don’t know how strong that effect is.)

    Further, an enormous amount of slack is cut extremely tall youths who haven’t yet matured as basketball players. If you are 7 feet tall, you don’t have to stand out in high school to get a chance to play in college. You just have to show a moderate degree of coordination and energy and you’ll be given a chance to develop.

    High potential players can go to the NBA out of high school (although not anymore from now on), or after 1, 2, 3, or 4 years of college, or after playing in a minor league or in a less competitive overseas league.

    Now, the NBA has recently banned drafting players out of high school, even though great NBA stars like Moses Malone, Kobe Bryant, and Kevin Garnett never attended college. Many observers have argued that the decline of average years of college ball played in recent decades has caused deterioration in the knowledge of fundamental among NBA players.

    That’s because college basketball teams serve as finishing schools for raw young talents, but NBA teams are not well equipped to drill 19 year olds in basketball basics. So, in recent years a number of extremely promising basketball players who went in the NBA straight out of high school have failed to develop to their full potential because a) they aren’t taught fundamentals by pro coaches and b) they don’t get playing time.

    There are far, far more spots open on the starting line-ups of college basketball teams than pro basketball teams, so hopefully this reform will expand the bottleneck and keep it from turning into a hockey situation.

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  53. David Kane says:

    The more that I look at this, the more it seems clear that, while Dr. Levitt is correct that more NHL players are born in the first half of the year, this has nothing to do with the stars-are-made-not-born thesis of the article. In other words, the reason that there are more early-births is not that early-births get more practice against better opponents. Instead, early-births are more likely to get high profile spots which give them exposure for the NHL draft. They are more likely to be drafted than a similarly talented late-birth because the coaches and GMs have seen them play as (more highly developed) teenagers.

    In other words, the hockey draft is inefficient. Teams should draft fewer early-births and more late-births.

    How might we test this? Easy. The better the cohort of players, the less inefficient the market will be. Among the best players (those who get lots of ice time for several years in the NHL), there will be no meaningful difference in early-versus-late births. These players are judged accurately on their adult skills.

    Instead, the effect will be much greater in the bottom of the NHL pool. Younger players with not a lot of ice time are more likely to be judged and retained on the basis of their (inaccurately measured because of birth-month issues) performance in youth leagues.

    If I am correct, the effect will be smaller and/or non-existent among older, better players. Alas, I can’t get any of these data sources to provide a clean test of this hypothesis, but I was able to split the Sportsnet.ca data into two portions: Jan-Jun and Jul-Dec birthdates. When you do this, the default sort is by points scored.

    I picked 30 points as a reasonable threshold. Turns out that, among the 174 NHL players who have scored at least 30 points this season, 140 were born in Jan-Jul and 134 in Jul-Dec. (Of course, points scored is not the best measure. What about goalies and defensemen? And so on.)

    But, big picture, there is no birth-month effect among the top 1/3 of NHL players. This suggests to me that the birth-month effect is much more likely to be a draft inefficiency. You don’t see this in other sports because the draft process is better.

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  54. David Kane says:

    The more that I look at this, the more it seems clear that, while Dr. Levitt is correct that more NHL players are born in the first half of the year, this has nothing to do with the stars-are-made-not-born thesis of the article. In other words, the reason that there are more early-births is not that early-births get more practice against better opponents. Instead, early-births are more likely to get high profile spots which give them exposure for the NHL draft. They are more likely to be drafted than a similarly talented late-birth because the coaches and GMs have seen them play as (more highly developed) teenagers.

    In other words, the hockey draft is inefficient. Teams should draft fewer early-births and more late-births.

    How might we test this? Easy. The better the cohort of players, the less inefficient the market will be. Among the best players (those who get lots of ice time for several years in the NHL), there will be no meaningful difference in early-versus-late births. These players are judged accurately on their adult skills.

    Instead, the effect will be much greater in the bottom of the NHL pool. Younger players with not a lot of ice time are more likely to be judged and retained on the basis of their (inaccurately measured because of birth-month issues) performance in youth leagues.

    If I am correct, the effect will be smaller and/or non-existent among older, better players. Alas, I can’t get any of these data sources to provide a clean test of this hypothesis, but I was able to split the Sportsnet.ca data into two portions: Jan-Jun and Jul-Dec birthdates. When you do this, the default sort is by points scored.

    I picked 30 points as a reasonable threshold. Turns out that, among the 174 NHL players who have scored at least 30 points this season, 140 were born in Jan-Jul and 134 in Jul-Dec. (Of course, points scored is not the best measure. What about goalies and defensemen? And so on.)

    But, big picture, there is no birth-month effect among the top 1/3 of NHL players. This suggests to me that the birth-month effect is much more likely to be a draft inefficiency. You don’t see this in other sports because the draft process is better.

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  55. SteveSailer says:

    This has been a very helpful discussion, and we seem to be making some progress.

    In general, I would suggest that blogging is Dr. Levitt’s natural strong suit. He would contribute more to the advancement of human knowledge if he would toss his ideas out on his blog first and let them be analyzed by intelligent, skeptical observers like Bill L. Lloyd. Only after they’ve been kicked around should he go on and formally publish them.

    Instead, Dr. Levitt tends to send his half-baked ideas first to the New York Times or economics journals. This means that when one of his ideas turns out not to be true, it has often already become part of the conventional wisdom and it’s too late to recall it.

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  56. SteveSailer says:

    This has been a very helpful discussion, and we seem to be making some progress.

    In general, I would suggest that blogging is Dr. Levitt’s natural strong suit. He would contribute more to the advancement of human knowledge if he would toss his ideas out on his blog first and let them be analyzed by intelligent, skeptical observers like Bill L. Lloyd. Only after they’ve been kicked around should he go on and formally publish them.

    Instead, Dr. Levitt tends to send his half-baked ideas first to the New York Times or economics journals. This means that when one of his ideas turns out not to be true, it has often already become part of the conventional wisdom and it’s too late to recall it.

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  57. joshua says:

    I think there may be another factor that comes into play due to the predominant nationality of NHL players, Canadians.

    We have fairly varied seasons up here north of 49, and the activities involved in making babies tend not to be as enjoyable on cold winter nights. If sex is seasonal, activity in June, July and August would help explain the bump in Jan-Feb

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  58. joshua says:

    I think there may be another factor that comes into play due to the predominant nationality of NHL players, Canadians.

    We have fairly varied seasons up here north of 49, and the activities involved in making babies tend not to be as enjoyable on cold winter nights. If sex is seasonal, activity in June, July and August would help explain the bump in Jan-Feb

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  59. David Kane says:

    1) Although births in Canada are somewhat seasonal (1% lower from Nov-Feb), there is no reason to worry that this is driving the results.

    2) Using the Sportsnet.ca site, it seems that the birth-month effect is just as strong among older players as it is among young players. For example, of the 284 players who are 30 years old or older, 161 were born in the first half of the year and 123 were born in the second.

    Hmmm. I would have guessed that older players would be evaluated more efficiently than younger players and so we should not see a birth-month effect. Then again, a different way of looking at the problem is to note that all 30+ year olds had to go through the same inefficient draft. In that draft, a lot of the late-borns that are really as good as their early-born peers were (incorrectly) weeded out. They never get a chance to compete at age 30.

    In other words, if the draft is inefficient, we should expect month-bias to persist even in the older players. The NHL evaluates older hockey players correctly, but the missing late-borns are no longer around to be evaluated.

    Does that make sense or am I telling Just-So stories about a result that I did not expect to see?

    Freakonomics, indeed.

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  60. David Kane says:

    1) Although births in Canada are somewhat seasonal (1% lower from Nov-Feb), there is no reason to worry that this is driving the results.

    2) Using the Sportsnet.ca site, it seems that the birth-month effect is just as strong among older players as it is among young players. For example, of the 284 players who are 30 years old or older, 161 were born in the first half of the year and 123 were born in the second.

    Hmmm. I would have guessed that older players would be evaluated more efficiently than younger players and so we should not see a birth-month effect. Then again, a different way of looking at the problem is to note that all 30+ year olds had to go through the same inefficient draft. In that draft, a lot of the late-borns that are really as good as their early-born peers were (incorrectly) weeded out. They never get a chance to compete at age 30.

    In other words, if the draft is inefficient, we should expect month-bias to persist even in the older players. The NHL evaluates older hockey players correctly, but the missing late-borns are no longer around to be evaluated.

    Does that make sense or am I telling Just-So stories about a result that I did not expect to see?

    Freakonomics, indeed.

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  61. To Steve Sailer

    you wrote:

    “Instead, Dr. Levitt tends to send his half-baked ideas first to the New York Times or economics journals. This means that when one of his ideas turns out not to be true, it has often already become part of the conventional wisdom and it’s too late to recall it.”

    I would love to take credit for these ideas, but they are not mine. I am just the messenger on this one.

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  62. To Steve Sailer

    you wrote:

    “Instead, Dr. Levitt tends to send his half-baked ideas first to the New York Times or economics journals. This means that when one of his ideas turns out not to be true, it has often already become part of the conventional wisdom and it’s too late to recall it.”

    I would love to take credit for these ideas, but they are not mine. I am just the messenger on this one.

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  63. SteveSailer says:

    One way to think about this is the concept of a bottleneck effect. How often does a youth with professional potential end up sitting on the bench as a teenager because there is another teen with pro potential starting ahead of him?

    I would guess that there are large differences in the size of the bottleneck for different sports and different positions. For example, if you have potential to make it to the major leagues as an outfielder, you are almost certain to get a lot of playing time in high school, since very, very few high schools have four more major league potential outfielders.

    On the other hand, if you want to be an NFL quarterback, it can be a good idea to attend a quarterback factory like mighty Hart H.S. in Southern California. But, that’s a more severe bottleneck because you might very well end up sitting on the bench throughout your entire high school career because another NFL potential quarterback is starting ahead of you.

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  64. SteveSailer says:

    One way to think about this is the concept of a bottleneck effect. How often does a youth with professional potential end up sitting on the bench as a teenager because there is another teen with pro potential starting ahead of him?

    I would guess that there are large differences in the size of the bottleneck for different sports and different positions. For example, if you have potential to make it to the major leagues as an outfielder, you are almost certain to get a lot of playing time in high school, since very, very few high schools have four more major league potential outfielders.

    On the other hand, if you want to be an NFL quarterback, it can be a good idea to attend a quarterback factory like mighty Hart H.S. in Southern California. But, that’s a more severe bottleneck because you might very well end up sitting on the bench throughout your entire high school career because another NFL potential quarterback is starting ahead of you.

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  65. David Kane says:

    Dr. Levitt,

    If the birth-month effect in NHL hockey is due to more playing time at younger ages (rather than inefficiencies/mistakes in the NHL draft), why is the effect not present among the best 1/3 or so of NHL players?

    Thanks for participating in this interesting discussion.

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  66. David Kane says:

    Dr. Levitt,

    If the birth-month effect in NHL hockey is due to more playing time at younger ages (rather than inefficiencies/mistakes in the NHL draft), why is the effect not present among the best 1/3 or so of NHL players?

    Thanks for participating in this interesting discussion.

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  67. SteveSailer says:

    I think it’s very important when making pronouncements about the effect of nature and nurture on what makes people good at something to be very specific about answering the question “Good at what?” The answer is going to vary tremendously.

    For example, my friend James Flynn, of the famous Flynn Effect of rising raw IQ scores, has put forward a popular theory about how feedback effects can transform small genetic differencs into huge differences in real world performance. It’s a pretty good theory, but the example he has been using to illustrate his theory — basketball players — is about the worst he could have chosen:

    “Take those born with genes that make them a bit taller and quicker than average. When they start school, they are likely to be a bit better at basketball. The advantage may be modest but then reciprocal causation between the talent advantage and environment kicks in. Because you are better at basketball, you are likely to enjoy it more and play it more than someone who is bit slow or short or overweight. That makes you better still. Your genetic advantage is upgrading your environment, the amount of time you play and practice, and your enhanced environment in turn upgrades your skill. You are more likely to be picked for your school team and to get professional coaching.”

    Living in New Zealand, I fear that Dr. Flynn has forgotten that basketball players are not “born with genes that make them a bit taller,” they are born with genes that make then one to seven (!) standard deviations taller than the average man. He has promised me that he is going to stop using basketball players in his example and start using soccer players or golfers or somebody else of normal size, where his argument is not prima facie implausible.

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  68. SteveSailer says:

    I think it’s very important when making pronouncements about the effect of nature and nurture on what makes people good at something to be very specific about answering the question “Good at what?” The answer is going to vary tremendously.

    For example, my friend James Flynn, of the famous Flynn Effect of rising raw IQ scores, has put forward a popular theory about how feedback effects can transform small genetic differencs into huge differences in real world performance. It’s a pretty good theory, but the example he has been using to illustrate his theory — basketball players — is about the worst he could have chosen:

    “Take those born with genes that make them a bit taller and quicker than average. When they start school, they are likely to be a bit better at basketball. The advantage may be modest but then reciprocal causation between the talent advantage and environment kicks in. Because you are better at basketball, you are likely to enjoy it more and play it more than someone who is bit slow or short or overweight. That makes you better still. Your genetic advantage is upgrading your environment, the amount of time you play and practice, and your enhanced environment in turn upgrades your skill. You are more likely to be picked for your school team and to get professional coaching.”

    Living in New Zealand, I fear that Dr. Flynn has forgotten that basketball players are not “born with genes that make them a bit taller,” they are born with genes that make then one to seven (!) standard deviations taller than the average man. He has promised me that he is going to stop using basketball players in his example and start using soccer players or golfers or somebody else of normal size, where his argument is not prima facie implausible.

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  69. 110phil says:

    Suppose that at a very young age, the late-birth players have difficulty competing with the early-birth players, and drop out of the game.

    This would explain why, at the all-star level, there is less of an effect. The very best late-birth players may have been exceptional enough at a young age that they *could* compete in an early-birth environment. They therefore did not drop out of the game.

    If this theory is correct, players that get by on “raw talent” (as the commentators say) should show a lesser effect, and grinders that get by on “guts and hard work” should show a greater effect.

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  70. 110phil says:

    Suppose that at a very young age, the late-birth players have difficulty competing with the early-birth players, and drop out of the game.

    This would explain why, at the all-star level, there is less of an effect. The very best late-birth players may have been exceptional enough at a young age that they *could* compete in an early-birth environment. They therefore did not drop out of the game.

    If this theory is correct, players that get by on “raw talent” (as the commentators say) should show a lesser effect, and grinders that get by on “guts and hard work” should show a greater effect.

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  71. TartanBill says:

    David Kane

    The efficiency of the NHL draft cannot be measures by simply exmining birthdays of top scorers. Europeans often use a different age cut point (school year) and until very recently US players used a summer age cut. European transfers to the NHL are biased toward the elite player so are more likely to affect the top scorers than the league overall.

    It would also help to examine the effect of the cull at age 14. It is common wisdom (although I cannot find a guick verification source) that a very large proportion of children drop out of organized hockey and baseball by age 14. This is early enough that the elite programs that feed the professional ranks should have a birthdate biased pool of players. The points are that one cannot evaluate the efficiency of the draft without examining the profile of the selection pool, and there is a plausible selection bias in the pool.

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  72. TartanBill says:

    David Kane

    The efficiency of the NHL draft cannot be measures by simply exmining birthdays of top scorers. Europeans often use a different age cut point (school year) and until very recently US players used a summer age cut. European transfers to the NHL are biased toward the elite player so are more likely to affect the top scorers than the league overall.

    It would also help to examine the effect of the cull at age 14. It is common wisdom (although I cannot find a guick verification source) that a very large proportion of children drop out of organized hockey and baseball by age 14. This is early enough that the elite programs that feed the professional ranks should have a birthdate biased pool of players. The points are that one cannot evaluate the efficiency of the draft without examining the profile of the selection pool, and there is a plausible selection bias in the pool.

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  73. alegrego says:

    Dear Levitt and Dubner

    Sincerely when I first read the article I thought that the prediction does not going to work for Argentina and Brasil (I am from Argentina). I thought that the prediction will only work in those leagues that were like the ones in Europe. So I work to find out the empirical evidence for Argentina and Brasil Sub-20 teams. Well, surprising I found that you were right. In my analysis I list the birthday of all the players from Argentina and Brasil that participate in the last 3 World Cup Sub-20 (Argentina 2001 – Emiratos Arabes 2003 and Holanda 2005). Doing this I take into account the problem that the Fifa restriction was created in 1997.
    May be you want to take a look at it. I posted in my blog under the title “A Star is Made para Argentina y Brasil”: http://producciondevalor.blogspot.com

    Sincerely

    Alejandro Gregori
    alegrego@yahoo.com.ar
    http://producciondevalor.blogspot.com

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  74. alegrego says:

    Dear Levitt and Dubner

    Sincerely when I first read the article I thought that the prediction does not going to work for Argentina and Brasil (I am from Argentina). I thought that the prediction will only work in those leagues that were like the ones in Europe. So I work to find out the empirical evidence for Argentina and Brasil Sub-20 teams. Well, surprising I found that you were right. In my analysis I list the birthday of all the players from Argentina and Brasil that participate in the last 3 World Cup Sub-20 (Argentina 2001 – Emiratos Arabes 2003 and Holanda 2005). Doing this I take into account the problem that the Fifa restriction was created in 1997.
    May be you want to take a look at it. I posted in my blog under the title “A Star is Made para Argentina y Brasil”: http://producciondevalor.blogspot.com

    Sincerely

    Alejandro Gregori
    alegrego@yahoo.com.ar
    http://producciondevalor.blogspot.com

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  75. zbicyclist says:

    Do we see the birth month effect in, say, tenured economics professors?

    Certainly, one would expect the same sort of maturation differences to apply in learning to read, math, discussion in class, etc. A child a few months older than the rest of the class should be seen as brighter, get better grades, get better Iowa test scores, etc.

    What about “high draft choices” such as kids admitted to MIT?

    Certainly the birth order effect is strong in this arena (first children tend to be more academic; see, for example, Zajonc and Markus). There’s also lots of data within any college. It would be fairly easy to “back up” the admissions data and figure out the age the applicant was when entering first grade.

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  76. zbicyclist says:

    Do we see the birth month effect in, say, tenured economics professors?

    Certainly, one would expect the same sort of maturation differences to apply in learning to read, math, discussion in class, etc. A child a few months older than the rest of the class should be seen as brighter, get better grades, get better Iowa test scores, etc.

    What about “high draft choices” such as kids admitted to MIT?

    Certainly the birth order effect is strong in this arena (first children tend to be more academic; see, for example, Zajonc and Markus). There’s also lots of data within any college. It would be fairly easy to “back up” the admissions data and figure out the age the applicant was when entering first grade.

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  77. Westy says:

    Truly it seems a thorough academic study of this topic above and beyond what has already been done would be appropriate. Mining a tremendous amount of data would certainly allow us to reach some conclusions.

    It would be interesting to see such a study that took into account each professional player’s country of origin and the corresponding youth league cutoffs during their youth there.

    This study could be conducted on sports that draw from a large pool of players and for which average size is not an impediment, such as soccer, baseball, and hockey. I wonder if all 3 would show the same effect? What other sports might we be able to guess the same results would show in?

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  78. Westy says:

    Truly it seems a thorough academic study of this topic above and beyond what has already been done would be appropriate. Mining a tremendous amount of data would certainly allow us to reach some conclusions.

    It would be interesting to see such a study that took into account each professional player’s country of origin and the corresponding youth league cutoffs during their youth there.

    This study could be conducted on sports that draw from a large pool of players and for which average size is not an impediment, such as soccer, baseball, and hockey. I wonder if all 3 would show the same effect? What other sports might we be able to guess the same results would show in?

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  79. bostonwolf says:

    Maybe I missed where this information was posted, but as soon as I saw this article my first thought was “what is the distribution of births for the human race as a whole?”

    I know it is not evenly distributed over the course of the year. And does it differ per geographic region?

    I found this information on Bangladesh but could not find anything else

    http://www.bbsgov.org/s_census/131.html

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  80. bostonwolf says:

    Maybe I missed where this information was posted, but as soon as I saw this article my first thought was “what is the distribution of births for the human race as a whole?”

    I know it is not evenly distributed over the course of the year. And does it differ per geographic region?

    I found this information on Bangladesh but could not find anything else

    http://www.bbsgov.org/s_census/131.html

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  81. omaha says:

    An alternative explanation: Hockey fanatics and professional players simply may be too distracted during the season to start a family. The Jan-March window corresponds to 9 months after what are the first few offseason months of May-July. And the best place to develop a hockey player is in the home of a fanatic and a professional athlete.

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  82. omaha says:

    An alternative explanation: Hockey fanatics and professional players simply may be too distracted during the season to start a family. The Jan-March window corresponds to 9 months after what are the first few offseason months of May-July. And the best place to develop a hockey player is in the home of a fanatic and a professional athlete.

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  83. SteveSailer says:

    Another thing to keep in mind is that there are correlations between birth month and a variety of conditions such as schizophrenia. Gregory Cochran and Paul Ewald have suggested that at least some of the incidence of schizophrenia is caused by prenatal or postnatal infections. (Many infections are more likely to be incurred in one season rather than another — the flu season being a famous example.)

    Microbiologists are increasingly taking seriously the general Cochran-Ewald theory that natural selection would have eliminated most of the heritable genetic causes for diseases that are common and severe, while it wouldn’t necessarily provide us with protections from infectious causes of major diseases, because the germs that prey on us are evolving along with our defenses against them.

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  84. SteveSailer says:

    Another thing to keep in mind is that there are correlations between birth month and a variety of conditions such as schizophrenia. Gregory Cochran and Paul Ewald have suggested that at least some of the incidence of schizophrenia is caused by prenatal or postnatal infections. (Many infections are more likely to be incurred in one season rather than another — the flu season being a famous example.)

    Microbiologists are increasingly taking seriously the general Cochran-Ewald theory that natural selection would have eliminated most of the heritable genetic causes for diseases that are common and severe, while it wouldn’t necessarily provide us with protections from infectious causes of major diseases, because the germs that prey on us are evolving along with our defenses against them.

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  85. TartanBill says:

    I did not know of the correlation bewteen schizophrenia and birth month. Very interesting. If it’s related to infectious disease, it is more likely to correlate to season than calendar year. That is, we would expect the birth month effect to be similar for December and January.

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  86. TartanBill says:

    I did not know of the correlation bewteen schizophrenia and birth month. Very interesting. If it’s related to infectious disease, it is more likely to correlate to season than calendar year. That is, we would expect the birth month effect to be similar for December and January.

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  87. SteveSailer says:

    Here’s a quote from an abstract of a big study in Georgia:

    “A Georgia Medicaid database (N = 746,615) and statewide infectious disease tables were used to identify correlations. Medicaid recipients were divided into schizophrenia (n = 11,736) and non-schizophrenia (n = 734,879) groups. A ratio of schizophrenic recipients to non-schizophrenic recipients was calculated for each birth cohort represented by each month of the year from 1948-1965. Multiple regression analyses indicated a significant relationship between winter season and schizophrenia incidence. However, neither influenza nor measles was predictive of schizophrenia prevalence. These findings were made using one of the largest sample of schizophrenic individuals in the literature to date.”

    “Seasonality and infectious disease in schizophrenia: the birth hypothesis revisited.”

    Battle YL, Martin BC, Dorfman JH, Miller LS.
    http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10628526&dopt=Abstract

    So, the seasonality effect definitely exists for schizophrenia, even in a state like Georgia with mild winters, but it’s apparently not caused by flu or measles.

    And here is Cochran and Ewald’s important paper that puts these kind of facts within an overarching Darwinian framework: “The Infectious Causation of Disease: An Evolutionary Perspective.”

    http://www.isteve.com/Infectious_Causation_of_Disease.pdf

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  88. SteveSailer says:

    Here’s a quote from an abstract of a big study in Georgia:

    “A Georgia Medicaid database (N = 746,615) and statewide infectious disease tables were used to identify correlations. Medicaid recipients were divided into schizophrenia (n = 11,736) and non-schizophrenia (n = 734,879) groups. A ratio of schizophrenic recipients to non-schizophrenic recipients was calculated for each birth cohort represented by each month of the year from 1948-1965. Multiple regression analyses indicated a significant relationship between winter season and schizophrenia incidence. However, neither influenza nor measles was predictive of schizophrenia prevalence. These findings were made using one of the largest sample of schizophrenic individuals in the literature to date.”

    “Seasonality and infectious disease in schizophrenia: the birth hypothesis revisited.”

    Battle YL, Martin BC, Dorfman JH, Miller LS.
    http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10628526&dopt=Abstract

    So, the seasonality effect definitely exists for schizophrenia, even in a state like Georgia with mild winters, but it’s apparently not caused by flu or measles.

    And here is Cochran and Ewald’s important paper that puts these kind of facts within an overarching Darwinian framework: “The Infectious Causation of Disease: An Evolutionary Perspective.”

    http://www.isteve.com/Infectious_Causation_of_Disease.pdf

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  89. SteveSailer says:

    Let me try to sum up the implications of the hockey example and relate them to Dr. Levitt’s ambitious statements about the relative importance of nature and nurture.

    To be drafted for the NHL at age 18, a Canadian youth must pass through an ever narrowing funnel of selection. In particular, he must distinguish himself in youth hockey competitions at the national and world levels that are restricted to 17-and-under players. This gives an advantage to those 17-year-olds who are almost 18 compared to those 17-year-olds who have just turned 17.

    Let’s assume for the moment that this 59-41 difference in first half versus last half of the year birthdates in the NHL reflects a genuine difference in mature performance level rather than a market inefficiency, and that it stems solely from the early people getting better nurture than the late people.

    So, does this fact settle the nature vs. nurture debate inaugurated so long ago by Sir Francis Galton?

    Well, the nature glass is part full and part empty, just as the nurture glass is part full and part empty. But, what are the proportions?

    Very roughly speaking, one in every ten thousand Canadian males between 18 and 40 is playing in the NHL.

    One factor of who gets into the NHL appears to be the luck of the birth date. Somebody born in January is about 1.7 or so times more likely to make the NHL than somebody born in December. So, the odds for somebody with the good luck to be born early in the year might be 1/7,500 versus 1/12,500 for somebody born late in the year.

    So, that is a significant role for nurture, but not an overwhelming one, since what we are talking about is that subtle opportunity effects in a national sport like hockey in Canada matter mostly to the far right edge of the bell curve for athleticism.

    I think it’s absolutely safe to say that nobody in the NHL is less than one standard deviation above the mean in natural athleticism, which eliminates 84% of the population. All the training in the world will never make a mediocre or below average athlete into an NHL player.

    Further, I would guess that almost nobody in the NHL is less than two standard deviations above the mean (although I could be wrong), so that would be 97.7% of the population doesn’t have a chance.

    Among the remaining 2.3%, however, I would imagine that nurture is highly important.

    Keep in mind, though, that ice hockey in Canada is of course one of the most competitive selection environments in the world. In less popular sports, however, flukes of environment matter far more.

    For example, in the 1970s, an American college student read that Team Handball would be an official sport at the 1976 Olympics. So, he convinced his fraternity brothers to take up the game and practice it for a few years. The fraternity qualified en masse to represent America in Team Handball in Montreal, and presumably had a blast (at least while they weren’t getting thrashed on the court by countries that care about the sport).

    The mean natural athleticism of those fraternity brothers was probably only slightly above average, but in the utterly non-competitive environment of the Team Handball in the USA 30 years ago, they were able to leverage their nurture advantage to become the best in America.

    So, this comparison reflects a general principle that the the more meritocratic and competitive a competition becomes, the more nature outweighs nurture.

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  90. SteveSailer says:

    Let me try to sum up the implications of the hockey example and relate them to Dr. Levitt’s ambitious statements about the relative importance of nature and nurture.

    To be drafted for the NHL at age 18, a Canadian youth must pass through an ever narrowing funnel of selection. In particular, he must distinguish himself in youth hockey competitions at the national and world levels that are restricted to 17-and-under players. This gives an advantage to those 17-year-olds who are almost 18 compared to those 17-year-olds who have just turned 17.

    Let’s assume for the moment that this 59-41 difference in first half versus last half of the year birthdates in the NHL reflects a genuine difference in mature performance level rather than a market inefficiency, and that it stems solely from the early people getting better nurture than the late people.

    So, does this fact settle the nature vs. nurture debate inaugurated so long ago by Sir Francis Galton?

    Well, the nature glass is part full and part empty, just as the nurture glass is part full and part empty. But, what are the proportions?

    Very roughly speaking, one in every ten thousand Canadian males between 18 and 40 is playing in the NHL.

    One factor of who gets into the NHL appears to be the luck of the birth date. Somebody born in January is about 1.7 or so times more likely to make the NHL than somebody born in December. So, the odds for somebody with the good luck to be born early in the year might be 1/7,500 versus 1/12,500 for somebody born late in the year.

    So, that is a significant role for nurture, but not an overwhelming one, since what we are talking about is that subtle opportunity effects in a national sport like hockey in Canada matter mostly to the far right edge of the bell curve for athleticism.

    I think it’s absolutely safe to say that nobody in the NHL is less than one standard deviation above the mean in natural athleticism, which eliminates 84% of the population. All the training in the world will never make a mediocre or below average athlete into an NHL player.

    Further, I would guess that almost nobody in the NHL is less than two standard deviations above the mean (although I could be wrong), so that would be 97.7% of the population doesn’t have a chance.

    Among the remaining 2.3%, however, I would imagine that nurture is highly important.

    Keep in mind, though, that ice hockey in Canada is of course one of the most competitive selection environments in the world. In less popular sports, however, flukes of environment matter far more.

    For example, in the 1970s, an American college student read that Team Handball would be an official sport at the 1976 Olympics. So, he convinced his fraternity brothers to take up the game and practice it for a few years. The fraternity qualified en masse to represent America in Team Handball in Montreal, and presumably had a blast (at least while they weren’t getting thrashed on the court by countries that care about the sport).

    The mean natural athleticism of those fraternity brothers was probably only slightly above average, but in the utterly non-competitive environment of the Team Handball in the USA 30 years ago, they were able to leverage their nurture advantage to become the best in America.

    So, this comparison reflects a general principle that the the more meritocratic and competitive a competition becomes, the more nature outweighs nurture.

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  91. Andi says:

    What if there are other valuable ends for athletes besides becoming pro hockey players you’re not considering? Getting a cheerleader to help you with your homework? Priceless.

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  92. Andi says:

    What if there are other valuable ends for athletes besides becoming pro hockey players you’re not considering? Getting a cheerleader to help you with your homework? Priceless.

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  93. TartanBill says:

    SteveSailor writes: “So, this comparison reflects a general principle that the the more meritocratic and competitive a competition becomes, the more nature outweighs nurture.”

    I think it depends upon the scale upon which you view it. Certainly to make the cut talent is an entry condition, but what separates the top performers? Say what you will about Barry Bonds and steroids, but his home run production jumped from upper tier to Ruthian after spending a very considerable (almost pathological) amount of time in the weight room. In the most highly competitive environments, perhaps talent is a necessary but not sufficient condition.

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  94. TartanBill says:

    SteveSailor writes: “So, this comparison reflects a general principle that the the more meritocratic and competitive a competition becomes, the more nature outweighs nurture.”

    I think it depends upon the scale upon which you view it. Certainly to make the cut talent is an entry condition, but what separates the top performers? Say what you will about Barry Bonds and steroids, but his home run production jumped from upper tier to Ruthian after spending a very considerable (almost pathological) amount of time in the weight room. In the most highly competitive environments, perhaps talent is a necessary but not sufficient condition.

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  95. alegrego says:

    Dear Levitt.

    Because I am from Argentina I try to probe itfor Argentina and Brasil and it works. Because the new law made by the FIFA is new I used the data for the Sub-20 teams of Argentina and Brasil of the last 3 Young FIFA World Cup Sub-20 (Argentina 01 – Emiratos Arabes 03 and Holanda 05). And I found the same empirical evidence I posted in my blog, maybe you want to see it.
    http://producciondevalor.blogspot.com

    Sincerely
    Alejandro Gregori

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  96. alegrego says:

    Dear Levitt.

    Because I am from Argentina I try to probe itfor Argentina and Brasil and it works. Because the new law made by the FIFA is new I used the data for the Sub-20 teams of Argentina and Brasil of the last 3 Young FIFA World Cup Sub-20 (Argentina 01 – Emiratos Arabes 03 and Holanda 05). And I found the same empirical evidence I posted in my blog, maybe you want to see it.
    http://producciondevalor.blogspot.com

    Sincerely
    Alejandro Gregori

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  97. Excuse me I thought that the first comment I made the machine lost it. That’s why I post the same two times.

    Alejandro

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  98. Excuse me I thought that the first comment I made the machine lost it. That’s why I post the same two times.

    Alejandro

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  99. beach says:

    zbicyclist,
    You may find this interesting this article, about the effect of surname initials on tenured economic professors, interesting:

    http://www.aeaweb.org/jep/contents/#9

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  100. beach says:

    zbicyclist,
    You may find this interesting this article, about the effect of surname initials on tenured economic professors, interesting:

    http://www.aeaweb.org/jep/contents/#9

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  101. prosa says:

    “Say what you will about Barry Bonds and steroids, but his home run production jumped from upper tier to Ruthian after spending a very considerable (almost pathological) amount of time in the weight room.”

    Excessive weight training frequently leads to a condition called “overtraining,” in which people actually begin to lose strength and size. It can be especially pronounced with someone Bonds’ age. And it should come as no surprise that use of steroids helps lessen the risk of overtraining.

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  102. prosa says:

    “Say what you will about Barry Bonds and steroids, but his home run production jumped from upper tier to Ruthian after spending a very considerable (almost pathological) amount of time in the weight room.”

    Excessive weight training frequently leads to a condition called “overtraining,” in which people actually begin to lose strength and size. It can be especially pronounced with someone Bonds’ age. And it should come as no surprise that use of steroids helps lessen the risk of overtraining.

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  103. zbicyclist says:

    Not sure anyone’s posted on this effect before, but certain mental illnesses are associated with particular birth months.(notably schizophrenia, peaking among those born from December through May)

    December through May overlap substantially with the hockey player peak months.

    Source: http://www.neoteny.org/a/birthmonth.html

    In terms of causal factors mentioned in these notes, they seem to pay no attention to cutoff dates — instead they pay attention to the seasonal variation in hormones (e.g. in the mother) due to factors such as the amount of daylight affecting the pineal gland.

    A quote: “The pineal gland, activated in the dark months, tends to suppress gonadal hormonal production. When it is suppressed, during periods of long days, sex hormones rise. We have already alluded to Badian’s (1983) report of a higher rate of nonrighthandedness in males conceived from December through May ”

    There are two alternative hypotheses, at least, wandering around here. If lefthanders are more common in December-May births, and if there is some advantage to being lefthanded in hockey (are NHL players closer to 50-50 Righhand-Lefthand than the general population is?) this could be part of the effect.

    The second hypothesis is concerned with hormones themselves. Might certain hormonal conditions in utero create the type of personality more likely to succeed as a hockey player? Seems possible.

    I’m out of my depth going much further with this research.

    On a net basis, there seems to be a paucity of evidence (largely NHL hockey players) and a variety of alternative hypotheses for the effect trumpeted in the Freakonomics article.

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  104. zbicyclist says:

    Not sure anyone’s posted on this effect before, but certain mental illnesses are associated with particular birth months.(notably schizophrenia, peaking among those born from December through May)

    December through May overlap substantially with the hockey player peak months.

    Source: http://www.neoteny.org/a/birthmonth.html

    In terms of causal factors mentioned in these notes, they seem to pay no attention to cutoff dates — instead they pay attention to the seasonal variation in hormones (e.g. in the mother) due to factors such as the amount of daylight affecting the pineal gland.

    A quote: “The pineal gland, activated in the dark months, tends to suppress gonadal hormonal production. When it is suppressed, during periods of long days, sex hormones rise. We have already alluded to Badian’s (1983) report of a higher rate of nonrighthandedness in males conceived from December through May ”

    There are two alternative hypotheses, at least, wandering around here. If lefthanders are more common in December-May births, and if there is some advantage to being lefthanded in hockey (are NHL players closer to 50-50 Righhand-Lefthand than the general population is?) this could be part of the effect.

    The second hypothesis is concerned with hormones themselves. Might certain hormonal conditions in utero create the type of personality more likely to succeed as a hockey player? Seems possible.

    I’m out of my depth going much further with this research.

    On a net basis, there seems to be a paucity of evidence (largely NHL hockey players) and a variety of alternative hypotheses for the effect trumpeted in the Freakonomics article.

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  105. zbicyclist says:

    Beach wrote: >

    Thanks! That was quite interesting (earlier surnames like A, B, have better success in economics, a field where joint authors are typically listed alphabetically).

    Luckily I’m not an economist and ZBicyclist isn’t my real name.

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  106. zbicyclist says:

    Beach wrote: >

    Thanks! That was quite interesting (earlier surnames like A, B, have better success in economics, a field where joint authors are typically listed alphabetically).

    Luckily I’m not an economist and ZBicyclist isn’t my real name.

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  107. syhu says:

    I would like to provide one more piece of evidence on this discussion using birth month data from baseball players in Taiwan.

    In Taiwan, the school year begins from September. All kids born after September the 1st will not be able to enroll the elementary school until the next academic year. The theory would suggest that the birth month of Taiwan’s atheletes is more concentraed in September, October, and November.

    The following is the distribution of the birth month of Taiwan’s professional baseball players (6 teams in total). You can see that the number of players born at the first three month (September, October, and November) of the school year is 49, while the number from the last three month (June, July, August) is only 26 players.

    Birth month / Number of players
    Jan. 12
    Feb. 14
    Mar. 20
    Apr. 7
    May 9
    June 8
    July 8
    Aug. 10
    Sept. 15
    Oct. 22
    Nov. 12
    Dec. 11

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  108. syhu says:

    I would like to provide one more piece of evidence on this discussion using birth month data from baseball players in Taiwan.

    In Taiwan, the school year begins from September. All kids born after September the 1st will not be able to enroll the elementary school until the next academic year. The theory would suggest that the birth month of Taiwan’s atheletes is more concentraed in September, October, and November.

    The following is the distribution of the birth month of Taiwan’s professional baseball players (6 teams in total). You can see that the number of players born at the first three month (September, October, and November) of the school year is 49, while the number from the last three month (June, July, August) is only 26 players.

    Birth month / Number of players
    Jan. 12
    Feb. 14
    Mar. 20
    Apr. 7
    May 9
    June 8
    July 8
    Aug. 10
    Sept. 15
    Oct. 22
    Nov. 12
    Dec. 11

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  109. dkane says:

    Allow me to be the first to connect this discussion to the full World Cup data for 2006. You can get the raw data from the official site. You can find a spreadsheet with the raw data plus my month calculations here.

    Comments:

    1) There is some minimal evidence for a birth-month effect. 74 World Cup players have birthdays in January, about 12 more than the 62 out of 736 that we might expect by chance. November (54) and December (56) are less common that we might expect.

    2) Splitting the sample into first part of the year (379) versus second part (357) is also consistent with the birth-month claims (ignoring different age cut-offs in different countries. But the percentage breaks (51.5% versus 48.5%) are hardly impressive. In an e-mail dialogue (before looking at this data), I had offered to bet Dr. Levitt $500 to the charity of his choice versus a signed copy of Freakonomics that fewer than 52% of World Cup players would be born in the first half of the year. He (wisely) declined to bet.

    3) Dr. Levitt writes:

    In Germany, the within country age cutoff is August 1. Thus, in soccer there are two different competitive pressures at work: one pushing towards more players born in the early months and the other towards more players in the later months.

    Interesting theory. Here is the data for the German team:

    Jan 1
    Feb 2
    Mar 0
    Apr 2
    May 3
    Jun 3
    Jul 0
    Aug 2
    Sep 2
    Oct 1
    Nov 7
    Dec 0

    23 players is too small a sample for much of anything, but there is no reason here to think that an August 1 cut-off in Germany affects anything.

    4) I need to do some more analysis, but my guess is that the very small effect is caused by a phenomenon similar to hockey. I would wager that some younger players who barely make the team are included because they star on youth teams in part because they are older than their peers. I bet that if we restricted attention to the 331 starting players, the effect would disappear completely.

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  110. dkane says:

    Allow me to be the first to connect this discussion to the full World Cup data for 2006. You can get the raw data from the official site. You can find a spreadsheet with the raw data plus my month calculations here.

    Comments:

    1) There is some minimal evidence for a birth-month effect. 74 World Cup players have birthdays in January, about 12 more than the 62 out of 736 that we might expect by chance. November (54) and December (56) are less common that we might expect.

    2) Splitting the sample into first part of the year (379) versus second part (357) is also consistent with the birth-month claims (ignoring different age cut-offs in different countries. But the percentage breaks (51.5% versus 48.5%) are hardly impressive. In an e-mail dialogue (before looking at this data), I had offered to bet Dr. Levitt $500 to the charity of his choice versus a signed copy of Freakonomics that fewer than 52% of World Cup players would be born in the first half of the year. He (wisely) declined to bet.

    3) Dr. Levitt writes:

    In Germany, the within country age cutoff is August 1. Thus, in soccer there are two different competitive pressures at work: one pushing towards more players born in the early months and the other towards more players in the later months.

    Interesting theory. Here is the data for the German team:

    Jan 1
    Feb 2
    Mar 0
    Apr 2
    May 3
    Jun 3
    Jul 0
    Aug 2
    Sep 2
    Oct 1
    Nov 7
    Dec 0

    23 players is too small a sample for much of anything, but there is no reason here to think that an August 1 cut-off in Germany affects anything.

    4) I need to do some more analysis, but my guess is that the very small effect is caused by a phenomenon similar to hockey. I would wager that some younger players who barely make the team are included because they star on youth teams in part because they are older than their peers. I bet that if we restricted attention to the 331 starting players, the effect would disappear completely.

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  111. dkane says:

    Not that anyone is still reading this thread, but a quick calculation reveals that neither the 10% of observations for January nor the 51.5% of observations for the first half of the year is statistically significant.

    There is no significant evidence that birth month affected one’s chances of playing in the 2006 World Cup.

    Will the New York Times be publishing a correction anytime soon?

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  112. dkane says:

    Not that anyone is still reading this thread, but a quick calculation reveals that neither the 10% of observations for January nor the 51.5% of observations for the first half of the year is statistically significant.

    There is no significant evidence that birth month affected one’s chances of playing in the 2006 World Cup.

    Will the New York Times be publishing a correction anytime soon?

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  113. Lobes says:

    From the FIFA World Cup Website:

    Italy’s Giovanni Trapattoni, meanwhile, relied on a greater power than ties, toothpaste or lucky numbers, and was often seen sprinkling holy water from a bottle provided by his sister, who is a nun. This practice caused controversy in Trapattoni’s homeland, but not nearly as much of a stir as the current France coach, Raymond Domenech’s admission that he takes players’ star signs into consideration before selecting his team.

    Scorpios, such as Robert Pires, are said to be the principal victims of this practice as, according to Domenech, “they always end up killing each other”. Nor can there be a surplus of temperamental Leos as they are liable “to try something daft”, a belief that Werder Bremen’s Johan Micoud blames for his omission from the French FIFA World Cup squad. “He (Domenech) was my coach at U-21 level, ten years ago, but apart from that I have never been contacted by him,” said Micoud. “Maybe I am not in the squad because my star sign is Leo and there are too many in the French team.”

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  114. Lobes says:

    From the FIFA World Cup Website:

    Italy’s Giovanni Trapattoni, meanwhile, relied on a greater power than ties, toothpaste or lucky numbers, and was often seen sprinkling holy water from a bottle provided by his sister, who is a nun. This practice caused controversy in Trapattoni’s homeland, but not nearly as much of a stir as the current France coach, Raymond Domenech’s admission that he takes players’ star signs into consideration before selecting his team.

    Scorpios, such as Robert Pires, are said to be the principal victims of this practice as, according to Domenech, “they always end up killing each other”. Nor can there be a surplus of temperamental Leos as they are liable “to try something daft”, a belief that Werder Bremen’s Johan Micoud blames for his omission from the French FIFA World Cup squad. “He (Domenech) was my coach at U-21 level, ten years ago, but apart from that I have never been contacted by him,” said Micoud. “Maybe I am not in the squad because my star sign is Leo and there are too many in the French team.”

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  115. harlant says:

    The article about whether a star is made to me is extremely true. I play soccer for a competitive soccer club and because of the cut off date I am allowed to play with the older team (the players which are in my grade-level) .At the same time since the cut off date is August 30 and I was born on August 26, it allows me to also play with the younger team. I find that when I play with the younger team, that I am not bigger by any means but that my mind is already a step ahead of them in what the next thing I should do on the field. Now, when I play with my team (the older one) I am just an average player, thinking just as fast or slow as they might be. The article above about NHL player I can not relate to but I do know cutoff dates have caused a lot of players to either move on or to be left behind. In Florida, the soccer Olympic Development Program (ODP) has a cutoff date which divides by year and this causes an issue because some players are in the higher grade level and are at a high playing level and some are in the grade below and are at a lower playing level because of the August cutoff date for travel soccer. This doesn’t seem like a huge issue until the player is in their junior or senior year and is trying out for the last time. These players that juniors but older have to try out with seniors who are getting ready to play at the college level. This doesn’t allow a fair chance for those juniors who are just as good as other juniors but not as good as those seniors. So overall I strongly agree that cutoff dates have a huge disadvantage but when is the time right to place a correct cutoff date? There will still be those who are at a disadvantage no matter what.

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  116. harlant says:

    The article about whether a star is made to me is extremely true. I play soccer for a competitive soccer club and because of the cut off date I am allowed to play with the older team (the players which are in my grade-level) .At the same time since the cut off date is August 30 and I was born on August 26, it allows me to also play with the younger team. I find that when I play with the younger team, that I am not bigger by any means but that my mind is already a step ahead of them in what the next thing I should do on the field. Now, when I play with my team (the older one) I am just an average player, thinking just as fast or slow as they might be. The article above about NHL player I can not relate to but I do know cutoff dates have caused a lot of players to either move on or to be left behind. In Florida, the soccer Olympic Development Program (ODP) has a cutoff date which divides by year and this causes an issue because some players are in the higher grade level and are at a high playing level and some are in the grade below and are at a lower playing level because of the August cutoff date for travel soccer. This doesn’t seem like a huge issue until the player is in their junior or senior year and is trying out for the last time. These players that juniors but older have to try out with seniors who are getting ready to play at the college level. This doesn’t allow a fair chance for those juniors who are just as good as other juniors but not as good as those seniors. So overall I strongly agree that cutoff dates have a huge disadvantage but when is the time right to place a correct cutoff date? There will still be those who are at a disadvantage no matter what.

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  117. Jef Simpson says:

    The birth data graph is one I prepared for my website for a study on the NHL that was done at the Cosmic Data-Bank. People steal my work and use it without any mention of its source. There is hardly anything one can do about it but I am starting to incorporate my website name into each graphic; getting wiser as I get older!
    The Cosmic Data-Bank has just celebrated its 20th anniversary. It is not an astrology site but for those who are only trained and not educated it may seem like an astrology site. The connections between humans and their solar system is largely unexplored because of astrology and its reputation as entertainment. Astrology did link us to the solar system and while most of the belief system of astrologers is as believable to me as the belief systems of those who believe in gods, our connection to the solar system is undeniable. It is our greater environment. Describing the connection is something that is attempted in earnest at the Cosmic Data-Bank and the results to date have been very encouraging. Yours truly, Jef Simpson, B.Sc., M.Sc., Vancouver, British Columbia, Canada.

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  118. Jef Simpson says:

    The birth data graph is one I prepared for my website for a study on the NHL that was done at the Cosmic Data-Bank. People steal my work and use it without any mention of its source. There is hardly anything one can do about it but I am starting to incorporate my website name into each graphic; getting wiser as I get older!
    The Cosmic Data-Bank has just celebrated its 20th anniversary. It is not an astrology site but for those who are only trained and not educated it may seem like an astrology site. The connections between humans and their solar system is largely unexplored because of astrology and its reputation as entertainment. Astrology did link us to the solar system and while most of the belief system of astrologers is as believable to me as the belief systems of those who believe in gods, our connection to the solar system is undeniable. It is our greater environment. Describing the connection is something that is attempted in earnest at the Cosmic Data-Bank and the results to date have been very encouraging. Yours truly, Jef Simpson, B.Sc., M.Sc., Vancouver, British Columbia, Canada.

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