Encyclopedic! I'll have to save this link.

FWIW, I recently heard of a movement within public health to NOT encourage helmets when bicycling. The rationale is that by encouraging helmets, they are implicitly discouraging biking by portraying it as dangerous (which depends on the roads) and a hassle. They say that biking without a helmet is healthier than not biking at all, due to the health benefits of regular exercise.