Motorcycle Helmets and Spine Injuries, Revisited
A recently published Johns Hopkins study concluding that motorcycle helmets reduce spine injuries elicited this response from a Maine-based economics professor whose own 1986 study suggested that the weight of a helmet could cause significant torque on the neck that would be devastating to the spine:
The recent publication of "Motorcycle Helmets Associated with Lower Risk of Cervical Spine Injury: Debunking the Myth" by Compton et al. (Journal of the American College of Surgeons, 2011) affords me the opportunity to reflect on the current state of the motorcycle helmet effectiveness debate on the twenty-fifth anniversary of my contribution to that literature. In 1986, I published a study, "The Effect of Motorcycle Helmet Use on the Probability of Fatality and the Severity of Head and Neck Injuries: A Latent Variable Framework" (Evaluation Review, 10:3, June).
The statistical analysis in that paper established the existence of a head-neck injury tradeoff in accident situations faced by the users of motorcycle helmets. In particular, helmets were found to exacerbate the severity of neck injuries past realistic critical impact forces to the helmet at the same time that helmets were found to reduce the severity of head injuries. As the title of the recent paper by Compton et al. implies, their study claims to have debunked the myth that helmets increase the risk of cervical spine (neck) injuries. They cite the source of the myth as my 1986 study. I respectfully disagree with their conclusion.
Far more important than the statistical results in my 1986 paper were the establishment of two methodological conditions that must be met to prevent regression estimates from systematically overstating (understating) the role of helmets in the reduction (exacerbation) of head (neck) injuries.
Unfortunately, in the intervening twenty-five years, the helmet effectiveness literature has been more concerned with overturning my results, by any means necessary, rather than taking the necessary methodological steps to obtain a valid assessment of helmet effectiveness. The current study, while more sophisticated than previous studies, is no exception.