Graves et al. Respond

We thank Salomon et al. and Cowling for their interest in our article on head injuries in cities with public bicycle share programs (PBSPs). Because these data were not based on exposure to bicycling (since such data do not exist), we purposely did not focus the analysis on changes in the rates of absolute number of bicycle-related head injuries. Instead, we examined the proportion of injuries to bicyclists that involved a head injury relative to other bicycle injuries. Salomon et al. in fact highlight why we stand by our data: in bike share cities there was a larger decrease in the number of nonhead injured bicyclists than in head injured bicyclists. Although Cowling calls attention to the decrease in the total number of bike injuries in the PBSP cities, her conclusion that bike safety has improved after the institution of the PBSP is not warranted without denominator data. Nor is there foundation for her speculation why the number of bike injuries in these cities may have decreased.

Our data are supported by 2 other important pieces of information. Helmets have been shown to decrease the odds of a head injury by as much as 85% in bicyclists involved in a crash,¹ and a study published in the Journal in 2012 by Kraemer et al. showed that only 15.7% to 33.1% of Washington, DC, bike share users wore helmets compared with 68.4% to 70.8% of those riding private bicycles.² Other studies observed similar patterns.^3–6

We agree that the study raises a number of questions that hopefully will be answered in prospectively collected studies.

References