Feds will stop hyping effectiveness of bike helmets
In 1989, a study in Seattle estimated that helmets prevent 85% of head injuries. Later efforts to replicate those results found a weaker connection between helmets and head injuries, but public health advocates, government web sites, and the news media often present it as fact.
Bad information can cause problems, even when it is promoted with the best intentions. If people think that helmets stop almost all head injuries, consumers will not demand better helmets, and legislators may feel it makes sense to require everyone to wear one. WABA asked two federal agencies to correct the misinformation, and after a lengthy process, they've agreed to do so.
How effective are bicycle helmets?In theory, helmets should absorb the shock from a crash. If your head strikes the ground or a vehicle, your brain could be seriously shaken by the sudden deceleration. With a helmet, the foam around your head forms a cushion. They can also prevent head fractures by spreading the force of the impact. It's like the difference between being hit on the head by a rock or a beach ball with the same weight.
It's hard to tell how often helmets actually prevent head injuries, however. Experiments on people are unethical, so instead researchers collect hospital data on people involved in bicycle crashes. In 1989, a team of researchers led by Dr. Robert S. Thompson, a preventative care specialist at the Group Health Cooperative of Puget Sound, collected data about cyclists in Seattle who went to area hospitals after a crash. Only 7% of the cyclists with head injuries wore helmets, but 24% of those without head injuries did wear helmets. Their statistical analysis, which was published in the New England Journal of Medicine, estimated that helmets had reduced the risk of a head injury by 85%.
Dr. Thompson's study was a "case-control study" like those that first found a link between smoking and cancer. There is no true "control" group, but epidemiologists say these studies are good for showing whether something has a good or bad effect on health, though not for quantifying it. Dozens of researchers sought to replicate the Thompson findings in their own communities. They also found that helmets reduce the risk of head injuries, but less frequently than Thompson's team found. Some studies even found that helmets increase the risk of neck injuries.
If you consider the entire body of research rather than just one study, and look at both head and neck injuries, helmets only reduce the risk of injury by about 15% to 45% . Nonetheless, public health advocates seized on the 85% estimate as a good way to communicate risk: failing to wear a helmet makes you more than 6 times as likely to experience a head injury. Government websites and newspapers have repeated it to the point where it has become ubiquitous in discussions about bicycle helmets.
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