Scientific evidence, eh? Proof? Wow. You need proof of benefit to do something that offers no harm, can ONLY do good (putting a layer between your bone and the asphalt)?

My last crash, that shattered my left collarbone and cost me seven weeks work and bike rides, would have been either fatal or profoundly debilitating had I not worn the helmet. My bell was RUNG, even with the thing! I don't need any more than that, folks. Even if my previous crashes hadn't hammered that point home....