Watson G S, Zador P L, Wilks A
Am J Public Health. 1980 Jun;70(6):579-85. doi: 10.2105/ajph.70.6.579.
Monthly mortality figures for motorcyclists for each state in the United States were obtained for the period January 1975 through December 1978. Twenty-four states revealed or weakened their helmet use laws at various dates within this period. Two of these states subsequently reintroduced a strengthened law. This paper measures the effects of these law changes on motorcyclist mortality. The states that repealed or weakened their helmet laws were matched with one or more states from the same geographic region that either did not have helmet use laws or did not change such existing laws in this four-year period. The effect of weakening the law in each state was then estimated in three steps: 1) the mortality data from each state for the period prior to repeal were regressed on smoothed data from the matched states; 2) these equations were used to predict the numbers of motorcyclist deaths that would have been expected in each state in the period following the repeal or weakening of the law if the laws had not been changed; 3) these numbers of expected deaths were then compared with the actual numbers of deaths that occurred. Of the 26 law changes, it was found that 23 resulted in a greater number of actual deaths in the period following the repeal or weakening of the law than were predicted to occur if the law had not been changed. It is estimated that the repeals or weakening of motorcyclist helmet use laws were typically followed by almost 40 per cent increases in the numbers of fatally injured motorcyclists.
获取了1975年1月至1978年12月期间美国各州摩托车手的月度死亡率数据。在此期间，有24个州在不同日期放宽或废除了头盔使用法律。其中两个州随后重新引入了强化法律。本文衡量了这些法律变化对摩托车手死亡率的影响。废除或放宽头盔法律的州与同一地理区域内一个或多个在这四年期间没有头盔使用法律或未更改现有法律的州进行匹配。然后分三步估计每个州放宽法律的影响：1）将废除前每个州的死亡率数据与匹配州的平滑数据进行回归；2）使用这些方程预测如果法律未更改，在废除或放宽法律后的时期内每个州预期的摩托车手死亡人数；3）将这些预期死亡人数与实际发生的死亡人数进行比较。在26次法律变化中，发现有23次在废除或放宽法律后的时期内实际死亡人数比如果法律未更改时预测的死亡人数更多。据估计，废除或放宽摩托车手头盔使用法律后，致命受伤摩托车手的数量通常会增加近40%。
