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Helmets, head injuries and “risk homeostasis”

April 11th, 2011

This week’s Jockology article in the Globe and Mail takes a look at helmets and the slippery concept of “risk homeostasis” — the idea that wearing protective equipment will cause you to take more risks and cancel out any safety benefits:

The message that Mikael Colville-Andersen offered to his audience at the TEDx conference in Copenhagen last November isn’t what you’d expect from a cycling advocate who travels the world promoting urban bike use.

“There are actually scientific studies that show that your risk of brain injuries is higher when you’re wearing a helmet, and that you have a 14-per-cent greater chance of getting into an accident with a helmet on,” he said. “These are not things that we hear about too often.”

With hockey head shots in the news, and revelations that ex-players like Bob Probert suffered from a form of brain damage called chronic traumatic encephalopathy, head protection is a hot topic. But Mr. Colville-Andersen’s controversial anti-helmet crusade offers a reminder that technology and equipment, on their own, can’t keep us safe. We have to consider the underlying factors that influence our risk-taking decisions – and those of the people around us… [READ THE WHOLE ARTICLE]

UPDATE April 11: Lots of e-mails and comments on the Globe site: this is clearly a controversial topic, so I’d like to expand on a couple of points. The truth is that I started working on this article with the idea of presenting the counterintuitive research that Mikael Colville-Andersen discusses in his TEDx talk, showing why helmets are actually a bad idea. But when I dug into the literature, I found that the picture was much more complicated than the way he portrayed it.

There are really two separate questions: physics and public policy. The first is fairly straightforward and asks whether, in the context of certain types of mishaps that sometimes occur on bicycles, a helmet will significantly reduce the severity of your injury. In the lab, we can clearly see that helmets can mitigate the effects of certain impacts. It’s much harder to show that this is the case in the real world, because we can’t have access to “controlled” scenarios of people going head-over-heels with and without helmets. And statistical studies of injury rates are hindered by all sorts of very serious limitations (e.g. we don’t actually know how cycling rates change, let alone traffic conditions, road surfaces, cycling skills, etc.)

Now, one could argue (as many people do) that the lack of crystal-clear epidemiological evidence of reduced cycling-related head injuries is PROOF that helmets don’t work. This is specious. Just because something is difficult to prove doesn’t mean that it’s not true. We can debate where the burden of proof should lie, but my personal assessment of the laboratory data, in combination with the admittedly circumstantial epidemiological data, is that there are certain situations in which I’d be very glad to have a helmet on my head. I certainly accept that other people might look at the same data I looked at and decide that helmets aren’t worthwhile – after all, risk calculation is a personal thing. But those who claim that it’s “proven” that helmets make no difference whatsoever in the context of individual accident scenarios are simply delusional, in my opinion.

Where Colville-Andersen is more convincing is in his public policy arguments, rooted in some of the factors I discuss in the article (risk homeostasis, safety in numbers, etc.). There have been dozens and dozens of studies on cycling injury rates and how they changed (or not) with the introduction of helmet campaigns and laws. My impression after reading through many of these studies: there are more studies supporting the efficacy of helmets than there are null studies, but the results are surprisingly weak and the overall conclusions are equivocal at best. All of the studies are plagued by serious methodological challenges inherent in trying to study this question. There are certainly plenty of studies that forcefully conclude that helmets are either good or no good, and plenty of people who cherry-pick those results in order to claim that the debate is settled one way or the other. But if you open both eyes and look at the totality of the data, I don’t believe there’s enough evidence to reach a conclusion either way.

And that leaves us with some interesting policy debates. If the overall effect of helmets is weak at best, are we justified in imposing a helmet law on children? How many cases of brain damage in Ontario would have to be avoided each year to make such a law worthwhile? One? Ten? 100? 0.1? These aren’t science questions, they’re policy questions. They’re worth debating – certainly, I’m more open to the idea of scrapping helmet laws than I would have been before watching Colville-Andersen’s talk. But as I concluded in the Globe article: based on what I learned from going through all this literature, I’ll still be wearing a helmet when I bike.

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