Ideally, to assess exposure to permissive MLDA policy, we would like to know where an individual dwelled when they were between the ages of 18 and 20. Unfortunately, this information is not available in vital statistics records, and so we use state of birth as a proxy. To check the accuracy of this approximation, we examined U.S. Census data on individuals who were between the ages of 18 and 20 during 1970 and 1980, the two census years that correspond to the historical period in which we are interested. Observed MLDA exposure was assessed based on their year and quarter of birth, and the state in which they resided at the time of census. We then imputed exposure under the assumption that state of birth was equivalent to state of residence at the time of census, and compared the proxy-imputed exposure with the observed exposure. From the total sample of N=196,620 observations, 72.4% resided in their state of birth, leaving 27.6% susceptible to misclassification when using the state-of-birth proxy. However, imputed MLDA exposure matched observed MLDA exposure in 88.0% of
