The association of age, sex and helmet use with the risk of death for occupants of two-wheeled motor vehicles involved in traffic crashes in Spain.

Abstract Background This study was designed to separate the association of age, sex and helmet use with the risk of death for occupants of two-wheeled motor vehicles (TWMV) involved in crashes into its two theoretical components: severity of the crash and occupant resilience. Methods We analyzed the retrospective cohort comprising all 48 016 pairs of drivers and passengers aged 14 years or more in TWMV involved in crashes with victims in Spain from 1993 to 2007 recorded in the Spanish traffic crash registry. The outcome (death or survival), age, sex and helmet use was known for both occupants. Adjusted relative risks (RR) for the association of age, sex and helmet with the risk of death were calculated with Poisson regression models. Results Each 1-year increase in age was related with a 3% increase in the risk of death related with lower resilience. The severity-dependent RR of death was 1.84 for male sex and 0.86 for non-helmet use, and the resilience-dependent RR was 0.72 and 2.53, respectively. Conclusions The direction and magnitude of the association between age, sex and helmet use and the risk of death of an occupant of a TWMV involved in a crash changed depending on which component of risk was considered: crash severity or occupant resilience. Specifically, female sex and non-helmet use seemed to be associated with crashes of lower severity, but together with increased age they were also related with lower resilience to the energy released in the crash, and therefore with a higher risk of death after adjustment for crash severity. This should be taken into account when assessing the association of individual factors with the risk of death after a crash.