The Dangers of N=1


From a reader named Mike Friedman:

I realized this morning that my daily behavior has been modified by a data point of one. I thought it would be interesting to you. Oh, and apologies in advance for the pun:

For the most part, my morning routine is the same every day. I shower, towel off, comb my hair, yada yada yada. A few weeks ago, while toweling off, I noticed a rather large spider on my towel. Being a little squeamish around spiders, I quickly threw down the towel and disposed of the intruding arachnid. I forgot about the “insect-dent” and went about my day.

Cut to this morning. After getting out of the shower and grabbing my towel, I experienced a moment of self-awareness and realized I was subconsciously checking my towel for spiders before applying it to my face. I realized in that moment of self-awareness that my behavior had been influenced by a single data point.

Consider the numbers: At 35 years old, I figure I have conservatively showered well over 12,500 times in my life, and I have only found one spider in my towel. And yet, for the last three weeks or so, I have been checking my towel every time I shower.

It got me thinking: How often do we allow our behavior to be influenced by single data points. Are there any positive examples?

Mike’s e-mail appealed to me because it touches on a lot of things that have been discussed here over the years, including recency bias, black swans, and the strange case of Baby Emily, whom we wrote about here:

In the early 1980′s, a group of psychologists and linguists banded together to write Narratives From the Crib, a study of how children acquire linguistic skills. Narratives was built around the speech patterns of one child, a 2-year-old girl. Her parents had noticed that she often talked to herself in the crib after they said good night and left her room. They were curious to know what she was saying, so they began to record her chatter. They turned on the tape recorder while they were tucking her in and then left it running.

Eventually they gave the tapes to a psychologist friend, who shared it with her colleagues. The big surprise to these experts was that the girl’s speech was far more sophisticated when she was alone than when she was speaking with her parents. This finding, as Malcolm Gladwell would later write in The Tipping Point, “was critical in changing the views of many child experts.”

The 2-year-old girl in question was referred to as Baby Emily. Her full name? Emily Oster. In retrospect, it would appear that Narratives From the Crib suffers what researchers call an “n of 1″ problem, with “n” representing the size of the sample set — a problem that is gravely exacerbated when the one subject turns out to be … well, a good bit brighter than average. Studying how children learn to talk by observing Baby Emily may be a bit like studying how children learn to play golf by studying Tiger Woods.

Leave A Comment

Comments are moderated and generally will be posted if they are on-topic and not abusive.



View All Comments »
  1. Alex says:

    Single data points are scientific no-no’s, but people and animals show single-trial learning all the time, especially in emotional contexts. They can be positive too; remember that time the cute waitress smiled at you and you didn’t get around to introducing yourself? You still think she has a thing for you.

    Thumb up 0 Thumb down 0
  2. Yu Ping Hu says:

    The obvious example is when someone will not go back to a restaurant where they’ve gotten sick from the food. Even for a place that follows all proper precautions, given the large number of patrons who eat at any given place, it’s probable that someone will get sick at some point. I’ve had friends swear off their favorite restaurants after a single incident.

    I can’t think of any positive examples, though.

    Thumb up 0 Thumb down 0
  3. Timothy says:

    Evolution works. We cannot afford to take two or three times to learn a lesson, so once we find something we dislike we immediately back away from it for all future circumstances. It might be bad science… but think how far away you are from swinging in a tree.

    Thumb up 0 Thumb down 0
  4. charles says:

    To steal from Taleb. I’m a turkey I’m happy and fed well for one thousand days along with my fellow Turkey’s, life is good. Then one day my buddy Sal get’s pulled from our pen and made into dinner (Thanksgiving). N is 1. It only takes N of 1 to revise my understanding of the world. The N of 1000+ has now been refuted. Taleb calls that domain extremistan (sp?). In any case it’s an important feature we’ve been gifted with from evolution. It’s a very good thing, and it’s also very bad for us. If you are aware of this..and almost nobody is in practice, even if they’ve read TBS or FBR, you’re ahead of the game. The key is pot odds as they say in cards, or the impact of the event (cost of checking towel) vs the cost of prevention (open it and take a look). In your case…no big deal, so you check.

    Now this post was of particular interest to me since I’m about the same age, and last year, for the first time in my life I had a spider hiding under my towel. I don’t care for them much either. Now get this…the next day same thing! You think you check your towels!

    Thumb up 0 Thumb down 0
  5. adam says:

    I learnt to not touch hot stoves after touching a hot stove only once.

    Thumb up 0 Thumb down 0
  6. jimi says:

    Pretty much everything that Congress does…..

    Thumb up 0 Thumb down 0
  7. terry says:

    Is gambling a “positive” example? ie: someone wins $20 on slots right off the bat, they keep trying to hit $20 again, but end up losing all their money.

    Thumb up 0 Thumb down 0
  8. Dave G says:

    @5- That is a little different. It would be a more reasonable comparison if you said you’ll never touch a stove again, hot or not, due to touching a hot stove once. The ratio of touching a hot stove to burning yourself is almost 100%, whereas the likelihood of having a spider on your towel (in Mike’s case) is likely a small fraction of a decimal point. Though I wouldn’t really want to shower at Mike’s place now either :)

    Thumb up 0 Thumb down 0