A remaining concern is that cross-state migration could lead to a spurious association if persons at greater risk for developing a substance use disorder were more likely to have moved to a state with more lenient drinking age laws. To explore this hypothesis, we use evidence from the NLAES survey and from the US Census years 1970 through 2000 to investigate (1) the prevalence of cross-state migration (2) the prevalence of a change in apparent MLDA exposure status when this is calculated based on state of birth or state of current residence, and (3) whether MLDA exposure based on state of birth is a better predictor of current substance use disorder, than MLDA exposure based on current state of residence.
