Statistic of how many head injuries you get if your head is smashed against a car door or the ground at high speed?
I suggest you make the experiment, because, I can only guess it hurts every time, and uhm, that's not backed by any statistic.
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I'm not allowed to reply because this has been down-voted, so i'll reply here:
the study you linked is a net result of people NOT riding bicycles because they don't want to ride if they have to wear a helmet. Thus they die "faster" from lack of exercising. That's twisted crap, IMO. It doesn't mean not wearing a helmet is safer. It means: NOT DOING EXERCISE IS UNHEALTHY. That's a very different thing. Note that everyone else "against helmets" in the HN threads linked to similar stats (!)
As I wrote, I'm all for people being allowed to wear one, or not wear one. But at the end of the day, it's safer to wear one in many environments such as SF/NYC/Paris (yes, Paris too It's not like Amsterdam, at all.).
But since you like stats, here are stats, that helmets protected 85% of helmet-wearing riders, as this study does not compare to "people who wouldn't ride because the think a helmet is ugly":
http://www.nejm.org/doi/full/10.1056/NEJM198905253202101?HIT...