Intended and Unintended Consequences of Youth Bicycle Helmet Laws
研究证实美国20多个州的青少年自行车头盔法减少了死亡并提高了头盔使用率，但也显著减少了青少年骑自行车行为，揭示了该政策的预期与非预期后果。
More than 20 states have adopted laws requiring youths to wear a helmet when riding a bicycle. We confirm previous research indicating that these laws reduced fatalities and increased helmet use, but we also show that the laws significantly reduced youth bicycling. We find this result in standard two-way fixed-effects models of parental reports of youth bicycling and in triple-difference models of self-reported bicycling among high school youths that explicitly account for bicycling by youths just above the age threshold of the helmet law. Our results highlight important intended and unintended consequences of a well-intentioned public policy.