[abakker]

I'm not sure it is appropriate to think about helmet use as having a bearing on life expectancy. The data on helmet accident avoidance is terrible. i.e. we have no idea what the severity of an accident "would have been" because that kind of data is never reported. Anecdotally, I've needed my helmet many times, but never reported its use to anyone.

you could theoretically look at the injury rate for non-helmeted people, but, again, you don't know how representative that rate is of the population. You are assuming that the non-helmeted accident statistics sample is representative of the cycling population. I am not sure that is true.

[edejong]

Almost everyone in the Netherlands is driving without. Should give a good comparative analysis.

[abakker]

Well, That is a very interesting example of why we can't compare populations. Many posts on HN have highlighted just how cycling-savvy the Dutch are both as cyclists and as motorists. Arguably, a Netherlands specific comparison would tell us something about whether helmets improved outcomes, but they wouldn't necessarily tell us anything about the rate, because falls may be less likely in the first place.

[colanderman]

Not really. Cycling is everpresent in the Netherlands (at least in Amsterdam); drivers are very aware of cyclists. Not at all true in the States.