A study is being presented in DC today at the Pediatric Academic Societies (PAS) annual meeting that claims that "bicycle helmets save lives, and their use should be required by law."
We conducted a cross sectional study of all bicyclists aged 0-16 years included in the Fatality Analysis Reporting System (FARS) who died or suffered an incapacitating injury between January 1999 and December 2009. The FARS defines an incapacitating injury as one that prevents a person from walking or normally continuing the activities the person was capable of before the injury. Date law enactment was obtained from several sources including the Insurance Institute for Highway Safety and the Governor's Highway Safety Administration. We compared rates of deaths/incapacitating injuries per age-specific state populations, between states with helmet laws and those without helmet laws. We used a clustered Poisson multivariate regression model to adjust for factors previously associated with rates of motor vehicle fatalities: elderly driver licensure laws, legal blood alcohol limit (< 0.08% vs. ≥ 0.08%), and household income.
To determine if such laws reduce national injury and death rates, Dr. Meehan and his colleagues analyzed data from the Fatality Analysis Reporting System on all U.S. bicyclists younger than 16 years of age who were severely injured or died between January 1999 and December 2009. They compared the injury and death rates in states with mandatory helmet laws to those without.
Of course there are problems with this becauseit just counts raw numbers.
It doesn't consider if states with mandatory helmet laws have less cycling, and of course there is evidence that mandatory helmet laws do reduce cycling. So we have the numerator (injuries/deaths) but not the denominator (cyclists or miles biked). Here is another study that showed the same thing, but considered the change in cycling.
In recent years, many states and localities have enacted bicycle helmet laws. We examine direct and indirect effects of these laws on injuries. Using hospital-level panel data and triple difference models, we find helmet laws are associated with reductions in bicycle-related head injuries among children. However, laws also are associated with decreases in non-head cycling injuries, as well as increases in head injuries from other wheeled sports. Thus, the observed reduction in bicycle-related head injuries may be due to reductions in bicycle riding induced by the laws.
In addition it doesn't consider what injury rates were before the laws were enacted. Maybe helmet laws are only enacted in states where there are a lot of cyclists, and states with a lot of cyclists are safer for cycling.
Finally, the second conclusion - that their use should be required by law - is some shocking bit of science. It ignorse the fact that we can determine that helmet use saves lives AND that laws mandating them are wrong. Sunscreen saves lives, we don't mandate it's use. Nor do we mandate condom use or bullet proof vest use. Universal organ donation would save lives, but we don't require it by law because there are other things we value in addition to - and even more than - saving lives.
Scientists should stay clear of these kinds of statements that require considering values in their official work. Saying that helmets save live and helmet laws save lives is something the data can (or not) defend. But saying we should value that over freedom or other concerns is total opinion. Scientists are free to weigh in with their opinion, they just should separate that which they can prove from that which they can not.