The Season of Death (Ep. 87)

(Photo: ornello_pics)

Our latest Freakonomics Radio on Marketplace podcast is called “The Season of Death.” The gist: Summertime brings far too many fatal accidents. But the numbers may surprise you.

(You can download/subscribe at iTunes, get the RSS feed, listen via the media player above, or read the transcript here.)

If you’re a longtime reader, you probably already have an idea of what we’re talking about. Human beings are, in general, quite bad at assessing risk. We tend to be scared of big, noisy, anomalous events – like shark attacks, which in an average year kill fewer than five people worldwide — while overlooking the seemingly quotidian reality of, say, drowning deaths (about 4,000 per year in the U.S. alone) and motorcycle fatalities (about 4,500 U.S. deaths annually). We have been exploring this idea since Freakonomics, where we asked whether a gun or a swimming pool is more “dangerous.”

In the podcast, we look into the death rate from four popular summertime activities: motorcycling, swimming, boating, and skydiving. Comparing such rates is rarely an apples-to-apples proposition but we do our best to sketch out the relative danger of each. You’ll hear from:

  • Randa Radwan Samaha, director of advanced research at the National Crash Analysis Center, which tracks motorcycle accidents;
  • Julie Gilchrist, a medical epidemiologist at the Centers for Disease Control and Prevention, which catalogs drowning deaths and the many other ways in which Americans die;
  • Mike Baron of the U.S. Coast Guard, which keeps a tally of recreational boating deaths; and
  • Nancy Koreen of the U.S. Parachute Association, which maintains a detailed online accident report. Koreen tells us that skydiving fatalities average about 22 per year, or 7 per 1 million dives, and that most fatalities are among experienced divers trying a difficult maneuver or watching out for their students — like these two instructors, who had 22,000 jumps between them. (Thanks to Jordan Pine for pointing us in this interesting direction, and for Kevin Boland for seconding the motion.)

Along we way, we ran across an interesting wrinkle in the motorcycle data. Take a look at this table from a National Highway Traffic Safety Administration report and see if you spot something hinky:

First of all, look at the massive spike in registered vehicles — from 4.9 million in 2001 to 8.2 million in 2010. We were told this was due in part to heavy marketing to (and purchases by) aging baby boomers reconnecting with their easy riding youth. Maybe, but still, that’s a big increase.

Then look at how the fatality rate increases significantly from 2001 to 2006. That could certainly fit the aging-boomer story. But then, thankfully, the fatality rate absolutely plunges — from 40.14 per 100 million vehicle miles traveled (VMT) in 2006 to 24.18 in 2007.

What happened? Did all those aging boomers with sub-par eyesight and reflexes decide en masse to keep their bikes in the garage?

Apparently not. Look at how the motorcycle miles driven suddenly went through the roof that same year, from 12 billion in 2006 to 21.4 billion in 2007. Such a huge and sudden spike in miles driven can of course explain how death rate plummeted (even while the number of deaths rose by 337), but it also makes you wonder if these statistics are at all trustworthy.

Randa Samaha from the National Crash Analysis Center told us that motorcycle usage and crash data are widely understood to be imperfect. In recent years there have been adjustments in how those data are gathered, leading to radically different statistics. Consider this recent Transportation Research Board report:

“There appears to be no uniformity of motorcycle VMT estimation method among the states, and no validation of the accuracy of various methods … For example, VMT estimates showed little fluctuation from 1982 – 2002, even though in the mid-1990s motorcycle registrations and fatalities dropped to approximately two-thirds of their 1982 levels. Motorcycle VMT estimates declined 10% between 1999-2002, even as motorcycle registrations increased by 20%, sales of new motorcycles soared by 63%, and motorcycle fatalities rose by 68%.”

So it’s possible that motorcycle riding is a) even more dangerous than the numbers say; or b) much less dangerous than the numbers say. Even if b) is true, however, it is still plainly dangerous — especially when it’s done without a helmet.



I wonder if there are significant differences in the fatality/injury numbers when you take into account the type of motorcycle being driven (I.e. sport vs cruiser). I'm sure age is also an influencing factor as to who drives what type of bike.


"we look into the death rate from four popular summertime activities: motorcycling, swimming, boating, and skydiving"

If boating includes personal watercraft surely those death statistics have increased more recently. Most recently rap star Usher's 11 year old son to the 50 year old former astronaut son of John Poindexter died from injuries or were killed due to personal watercraft accidents. Reading news reports from the coastal area where I grew up it seems like at least one person per month is killed in a boat or personal watercraft accident during the prime summer months of June, July, August.

"So it’s possible that motorcycle riding is a) even more dangerous than the numbers say; or b) much less dangerous than the numbers say. Even if b) is true, however, it is still plainly dangerous — especially when it’s done without a helmet."

Actually horseback riding is far more dangerous than motorcycle riding in either a per mile ridden or per hour use basis.

"The Season of Death.” is actually the winter as more people die from natural causes, accidents, etc during the winter than any other season. This is based on the fluctuations of casket production and sales as I had worked at a casket manufacturer in the past.


Enter your name...

I believe that summer is actually the most dangerous, because of heat-exacerbated deaths. Coffin sales aren't necessarily a reliable indicator these days, because so many people choose cremation.


For a fair risk analysis, you really should compare the death rates (and injury, hospitalization, etc) of the various activities to the couch potato baseline. Yeah, I may face an increased risk of dying from riding the horse, swimming (with or without sharks), bike riding, &c, but I think that's more than counterbalanced by my decreased risk of death from the consequences of obesity, or just sitting:

As you say, humans are bad at assessing risk :-)


Wasn't 2007 (and 2008) a year of rising gas prices? Is it possible people rode motorcycles more during those years to save money on gas? Overall lower numbers of cars on the road those years might explain the lower death rates. That's said I might have expected some reversion in 2009 and 2010.


I'm a bike commuter, and my ears perked up when I heard you jump from helmets and motorcycles to helmets and bicycles in the podcast. Here's what Dubner said (excerpted from the Marketplace story):

"To some people it is, to some people plainly it's not. I tend to agree with you, especially riding a bike without a helmet. Helmets are estimated to prevent about 40 percent of crash deaths among motorcyclists and yet there are a lot of bicyclists out there who would much prefer to ride a bike than to not and to ride a bike without a helmet. Look, if safety is your primary concern this summer -- I'm not saying it should be -- but if it is, I've got the ultimate activity for you and everybody out there. You stay in side, you listen to your radio."

I understand the point Dubner's making about motorcyclists, but I don't really understand the point he's making when he switches to bicyclists.

I wear a helmet when I ride a bike. But I bristle when I hear people get judgmental about people not wearing helmets while biking. Mandating helmets on motorcycles is one thing (much higher speeds, 100% on same roads as much larger cars, often highways), but helmets on bicycles is another thing entirely.

In this talk ( given at some European TED conference, a Swedish bike ambassador makes the case that a public campaign emphasizing helmet use resulted in a lower cycling rate in Sweden.

Of course, that is an unintended effect of a campaign which is based upon the premise that cycle with helmets is clearly safer than cycling without helmets. And that is the question.

When cycling, does helmet use make you much safer? What about breaking it down by types riding: e.g. in protected non-car paths, mountain biking, urban cycling, rural cycling, racing)? I can see it being necessary if the cycling is racing or if it shares roads with cars going at high speeds. However, helmet use seems to be accepted dogma, at least in the U.S. An examination of this dogma could be a perfect Freakonomics piece.



Also does using a bicycle helmet save a life but leave the rider more incapacitated?

This also has been argued for motorcyclists that helmet use contributes to surviving riders with more costly injuries. This is as if the issue is argued for pure money costs only not emotional or social costs.

[That said my personal choice is to always wear a non-modular full face helmet even though it is a distraction to put-on and pull-off my eyeglasses when starting and ending a ride. But I do not criticize any others choices in the face of risk whether it is riding a motorcycle without a helmet or piloting a private plane or crossing the street in the middle of the block...]

Mike B

I wonder if there is a subconscious evolutionary advantage in our way of assessing risk. If someone dies in a manner that they had some control over, such as drowning in a pool, then it improves the species as that those individuals predisposed to such a fate will be less likely to reproduce and over time traits that prevent accidental drowning, excess drinking or even unsafe driving will be eliminated from the gene pool.

Those events that tend to get a lot of play in the media often involve forces that are beyond anyone's control, like rampaging gunmen, severe weather, terrorism, etc. Those events that kill indiscriminately do little to improve the species and therefore we are instinctually predisposed to see them as a negative.


Wish you'd delve further into the question of just accurate some of these statistics can be. I do wonder, when I see some of them, whether they're not just being pulled out of thin air to make a point. Take motorcycles, for instance. Motorcycle registrations and sales, sure, but who tracks bikes being junked, or purchased in an "I wanna be a biker dude" moment, ridden a few hundred miles, then parked in the garage for several years until someone like me comes along and buys them cheap? And how on Earth can anyone expect to come up with a reliable figure for miles ridden?

Same applies to boats and personal watercraft. How do you determine how much they're being used, which is the determining factor in risk? My friends have had their boat out once this year; the neighbors have a boat and jet ski (both bought in an excess of consumerism, along with the RV) that I know for a fact haven't been in the water for at least four years. How do they factor into boating risk calculations?


Ian M

I wonder if the large 2006-2007 jump in motorcycle miles can be explained by a large increase in touring?
If so, what could have caused the touring increase?
Is riding with other motorcyclists less likely to result in injury? (Less stunt riding, easier to see a large group, etc?)

Was there a large shift in the type of motorcycle contributing to these miles? Anyone who rides knows that lumping all motorcycles together into one ball is nonsense. Even my wife knows that. (Yes, you can get a motorcycle. No, you can't get a sport bike.)
Who knows what is considered a motorcycle in these stats. Is a scooter a motorcycle? I would bet that a lot more miles have been being put on scooters as the price of gasoline goes up.

Stats without information is bad stats. Garbage in = garbage out.

Joel Upchurch

I did my first calculations on motorcycle fatalities 20 years ago. One basic thing is that comparing vehicle mile to vehicle mile puts a crimp in the statistic because motorcycles generally have less passengers per vehicle. If you want to compare motorcycle to cars, you need to increase the numbers by at least 40% for motorcycles. Numbers for bicycles are SWAG, because bicycles don't usually have odometers and also don't use fuel.

If you actually look at fatalities for pedestrians, Bicyclists and motorcyclists, the fatality rate for people actually inside car and trucks is actually below 1 fatality per 100 million miles.


I work in the area of gov't health statistics, and occasionally we see anomalous year-to-year changes in rates/counts of things. Typically. . .

1) It might have just happened that way. Odd but can happen.
2) There was some real-world reclassification in the data. E.g. maybe off-road dirt bikes were re-coded as motorcycles in 2007 by FHA. But, the coding done by doctors had always classified dirt bikes as motorcycles, so that number didn't jump.
3) PEBKAC. E.g. some person had the data broken into "males" and "females" and kept running their "miles" database with the "males only" selection made, but the "fatalities" database had "males" and "females" selected. Someone noticed this in 2007 and didn't correct previous years. When a process is established, and believed to be correct, errors can persist for years in something like that.
4) There was a new method created for calculating highway miles, and they had no way to retrofit the new method to the old data, or they didn't want to publish a retraction.



Another thing you seem to have overlooked here is that many risks are not actually constant over the population, even though they're presented that way. For instance, I would expect that swimming pool deaths are highest among young children, poor and non-swimmers, people apt to clown around pools while intoxicated, etc. Since I'm an adult, an expert swimmer, and a very light drinker, I have adjusted my risk from swimming pools to be much lower than the population average. By contrast, my risk of shark attack, should I choose to swim in water inhabited by sharks, is entirely out of my control.


Re: your last quip regarding the safety of sitting at home listening to the podcast being the safest of all things.... I've actually heard it said that you, statistically speaking, have less chance of dying on a plane than sitting in your home watching TV. So you should tell people if they want a safe summer, get the podcast (why not?) and go get on a plane.

Jonathan Roseland

You know what I haven't ever skydived drunk but I have skydived very hungover and it is THE ULTIMATE CURE for a hangover... haha!