Many doctors believe that enforced bicycle helmet laws improve health, but others who argue the other way set this view aside.
Several studies suggest that cyclists who choose to wear helmets have fewer head injuries than non-wearers. But Dorothy Robinson, Senior Statistician at the University of New England, New South Wales, Australia, argues that there is no clear evidence that bicycle laws improve public health.
She reviewed data from countries that have legalised the wearing of helmets and believes that the data indicate that helmet laws discourage cycling and produce no obvious response in percentage of head injuries.
For example, in New South Wales, legalisation increased adult use of helmets from 26% in 1990 to 77% and 85% in 1991 and 1992. Yet, she argues, the rate of decline of head injuries did not change.
This contradiction may be due to risk compensation, incorrect helmet wearing, reduced safety in numbers (injury rates per cyclist are lower when more people cycle), or bias in case-control studies, says Robinson.
She suggests that helmet laws are counterproductive and that governments should focus on factors such as speeding, drink-driving, failure to obey road rules, poor road design, and cycling without lights at night.
Robinson's arguments against helmet legislation are flawed, argue four professors of epidemiology from Canada and the US.
They challenge her interpretation of the data she presents and point to several independent studies showing a protective association between wearing bicycle helmets and head injuries. They also refer to studies showing a reduction in head injuries after helmet legislation was enacted.
Their analyses of the data from New South Wales show that, as the proportion of helmeted cyclists increases, the proportion of bicycle related head injuries decreases.
They also question Robinson's preference for time series studies, which address populations, as opposed to case-control studies, which involve individuals, arguing that the latter provide much stronger evidence. The North American experts dismiss her argument for risk compensation as "pure speculation."
Finally, they conclude that, without data about how long and how fast riders who quit rather than wear helmets following legislation, "Robinson cannot conclude that decreases in cycling are harmful to health."