You mentioned a study... has this been tried?

I agree that if someone is going to wack me on the head with a hammer, I'd rather have a helmet on... but this is an unlikely occurance while riding. When you crash there are lots of things going on, and in many situations I can see helmets being detrimental. At any rate we should see an overall reduction in serious head injuries and fatalities when helmets are used, if they *worked*... and we don't. So there must be something going on that makes helmets ineffective.