Covariates included variables that were available in both the mortality and population data sources: year of birth, state of birth, whether the subject resided in their birth-state at time of death or census, year of death or year of census, sex, educational attainment, and race/ethnicity. Educational attainment was collapsed into a binary variable indicating more than 12 years of education (equivalent to a high school degree) or 12 or fewer years of education. Race/ethnicity was categorized as non-Hispanic White, non-Hispanic Black, and Hispanic categories. A dichotomous variable to indicate whether an individual resided in their birth state at time of death or census was created by comparing state of birth and state of residence variables. This variable was used as a measure of the likelihood that a person resided in their birth state when they were between 18- and 21-years-old. Those who resided in their state of birth as adults were assumed to be more likely to also have dwelled in their home state during early adulthood, although this does not preclude the possibility that such individuals left their state
