Question:
One similarity is that certainly the helmet increases the effective size of the head, whether it's a football helmet or a bike helmet.

A football helmet is much larger than a bicycle helmet and covers a *much* larger part of the head. My point is that pro-helmet groups will grab any fatality data they can find and claim that helmets would reduce _all_ fatalities by 85%, based on the most optimistic study ever done, even though it looked at mostly minor head injuries. This has even been done in at least one paper in a refereed journal! It's obviously garbage - but when a website refutes it by giving more data, you're saying _we_ should talk only about head injuries! How are we to refute _their_ arguments about all fatalities unless _we_ talk about all fatalities?? A plastic hat that envelops the head to protect from one type of impact is not similar to a plastic hat that envelops the head from another type of impact? The fact that both increase the size of the head is not similar?

Answer: I'm having a problem figuring out what you're saying here. It would appear that to you no change in fatalities would mean that instead of bicyclists being killed by head injuries they simply are being killed by other injuries.

OK, let's examine that idea. It turns out that in truly serious accidents there are usually a number of 'fatal' injuries to the victim. So some people claim that helmets will save your head? Even if they did it would in all likihood make not a wit of difference in the statistics since the cases where a cyclist is killed he would have been equally dead with or without a head injury.

And it also appears that death from head injury and head injury alone are pretty rare occurences. Since you obviously haven't read the study you can be excused for not understanding that they didn't consider any specific helmet but the IDEA of helmets in that study. And it wasn't American football at all that they were talking about but Australian football. Something much more akin to soccer with teeth.

Please note that a bicycle helmet is indeed about the same size as a football helmet designed for use in soccer and rugby. Moreover, the odd shape of a bicycling helmet in order to make it more fashionable probably has a deleterious effect on it's efficacy, but who would know since the helmet 'standards' have been written to maximize helmet sales and not to form intelligent safety standards. Note that it isn't possible to make an "effective" helmet in the very first place (note that Dr. Shively of the Snell Institute make that statement himself) so making a standard from what is possible isn't as stupid as it may sound at first. While helmet standards don't even SUGGEST sufficent protection they do assure that rated helmets all meet the same minimum specification.