Lethal misconceptions: interpretation and bias in studies of traffic deaths

Clinical epidemiology studies are vulnerable to subtle confounding, leading skeptics to claim that an odds ratio below three rarely indicates a clinically important finding. We argue that such a high threshold is inappropriate when interpreting traffic death studies in clinical epidemiology research. We review 10 concepts that emphasize the value of modest effect sizes by taking into account the baseline frequency, nonfatal disability, numbers needed to treat, shared responsibility, event diversity, behavioral offsets, measurement error, indirect reinforcement, delayed progression, and economic affordability. An awareness of these concepts may help when interpreting effect sizes in studies of traffic deaths.