Most of the proof to wear a helmet while riding a bicycle falls in two categories: 1. 90% of people who died while riding a bike weren't wearing helmets. This argument proves the effectiveness of wearing helmets, but doesn't prove that bicycling is a dangerous enough activity to warrant wearing one. This point would be true for walking helmets too, but people don't wear helmets for walking because it's not dangerous. People don't wear helmets while riding in cars, even though it would save some lives. 2. Person X got hit with a car and her helmet shattered into a million pieces but they survived. These arguments are not really proof since it's a testimonial account (sure it's effective emotionally, as anyone who's seen infomercials will attest, but it's not proof). Additionally, helmets are designed to shatter when slight impacts occur, ones that wouldn't necessarily cause more than a bump on the head (so a shattered helmet doesn't mean the alternative is a shattered skull). What sort of evidence is needed to prove that helmets are necessitated? We need a comparison between the rates of head injuries that occur when people are bicycling and the rates of head injuries that occur when people are walking as pedestrians or riding in a car. Comparing simple numbers is not enough, since obviously a lot more people walk around than bike. The comparison must be done on a per-time basis. Additionally it needs to be specific to head injuries, since most bicycle accidents result in scrapes where helmets do nothing. I would be convinced to wear a helmet if it's more dangerous than both walking and driving a car, since I don't wear one for either of those activities. Some interesting things I found while researching this was that the Netherlands have the highest rate of people who bike and a ridiculously small rate of fatal accidents, even though helmets are almost unheard of. Additionally, in Australia after they mandated all bicyclers wear a helmet by law, less people ended up riding their bike. In fact, many claim that since riding your bike (exercise) helps prevent the #1 killer heart disease, more people have ended up dead as a result of the bicycle helmet law.