Risk compensation theory and voluntary helmet use by cyclists in Spain

Objective: To obtain empirical data that might support or refute the existence of a risk compensation mechanism in connection with voluntary helmet use by Spanish cyclists. Design: A retrospective case series. Setting: Spain, from 1990 to 1999. Subjects: All 22 814 cyclists involved in traffic crashes with victims, recorded in the Spanish Register of Traffic Crashes with Victims, for whom information regarding helmet use was available. Main outcome measures: Crude and adjusted odds ratios for the relation between committing a traffic violation and using a helmet. Results: Fifty four percent of the cyclists committed a traffic violation other than a speeding infraction. Committing a traffic violation was associated with a lower frequency of helmet use (adjusted odds ratio (aOR) 0.63, 95% confidence interval (CI) 0.58 to 0.69). Cycling at excessive or dangerous speed, a violation observed in 4.5% of the sample, was not significantly associated with helmet use either alone (aOR 0.95, 95% CI 0.56 to 1.61) or in combination with any other violation (aOR 0.97, 95% CI 0.79 to 1.20). Conclusions: The results suggest that the subgroup of cyclists with a higher risk of suffering a traffic crash are also those in which the health consequences of the crash will probably be higher. Although the findings do not support the existence of a strong risk compensation mechanism among helmeted cyclists, this possibility cannot be ruled out.