Originally Posted by
khutch
This is the second time this has been asked and in response I have to ask what is so magic about time? If you want to calculate your total lifetime probability of dying while cycling you can use your estimated total cycling mileage as easily as your estimated total time spent cycling. Per mile is a far more natural and just as accurate a way of presenting the data. I can tell you how many miles I have ridden my bikes, I have no idea how many hours.
If you don't want to believe the data then don't. It is less certain than automotive data since there are no collection points for bicycle odometer readings and no requirements that bicycles have them. The data we have are good faith estimates based on the best information available. I don't see any reason to reject it, I think it is good enough for the purpose at hand.
I'm more of a time guy, I guess. I know I spend 30-40 minutes per day commuting. Even if they were time based, I'd still consider the stats I've seen in this thread a very poor indicator of how likely a certain behavior is to result in brain injury. They're simply too vague. A chart relevant to this discussion would include injuries as well as deaths and require extensive data on road worthiness of all bikes involved, skill levels of all riders involved, condition of helmets used and whether helmets were properly fitted. Type of riding undertaken should also be reflected, ie: BMXing at the skatepark, DH MTBing, riding at a walking pace on the MUP, 15mph on the MUP (this one scares me to no end), riding solo on the road, riding in a paceline, current temperatures, etc.
I'm pretty confident that on a per minute basis, I'm FAR less likely to hit my head on my commute than someone who hits the MUP two or three Sundays every summer. On a per-mile basis, surely the delta is even larger but like I say, I'm a time guy, so that's how I like to think about it. I put my per minute probability of me hitting my head during a commute somewhere around that of an experienced jogger running on the same streets. So, taking those factors in to consideration, I only don the helmet on my commute when snow or ice threatens.
If you find the provided stats supply you with the information to gauge your head protection needs, that's fine, but please don't try to tell me they are adequate information for me to gauge my helmet needs.