Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
Existing econometric studies of the efficacy of motorcycle helmet laws assume that such laws are exogenously determined and may therefore yield biased results. To correct for possible selectivity bias, the authors specify and estimate a self-selection model in which the choice of having a helmet law is endogenous. Their results indicate selectivity bias exists and that if laws were randomly assigned, fatality rates for states with helmet laws would on average be less than one percent lower than for states without laws. Copyright 1991 by MIT Press.