Arguments against helmet legislation are flawed

doi:10.1136/bmj.332.7543.725

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Brent Hagel, assistant professor1,
Alison Macpherson, research scientist1,
Frederick P Rivara, professor of paediatrics1,
Barry Pless, professor of paediatrics, epidemiology, and biostatistics (barry.pless@mcgill.ca)1

¹ Montreal Children's Hospital Research Institute, Montreal, Canada

Correspondence to: B Pless

Robinson's opposition to helmet laws is contrary to published evidence on the effectiveness of bicycle helmets.1 At least six independent studies have reported a protective association between wearing bicycle helmets and head injuries.^w1-w6 Furthermore, systematic reviews of the relation have all noted a protective effect of helmets.2^–4 Similarly, six studies have examined the relation between helmet laws and head injuries, and all found a reduction in head injuries after legislation was enacted.^{w1 w7-w11}

What do the data show?

Robinson suggests that the percentage of bicycle related injuries that are head injuries seems to be declining and that this decline started before the enactment of the law. However, her figures also show that helmet laws are successful in increasing helmet use and seem to be associated with a decrease in the percentage of head injuries. The effect of helmet use is most evident in her fig 2, where the increase in the percentage of cyclists wearing helmets corresponds with a decrease in the percentage of head injuries. The correlation coefficient for the percentage helmet use and percentage head injury is −0.8 for children and −0.9 for adults. The corresponding r² of 0.64 for children and 0.81 for adults suggests that much of the variation in the percentage of head injuries is explained by helmet use. Thus, as …