The analytical approach exploits changes in policy within states over time, and differences in policy between states at any given time, to estimate the policy effect independently of state and time confounders. (Theory behind this approach is provided in the Supplemental Material). The general model is outlined in Equation 1, below. It expresses the outcome variable, Y, as a function of (left-to-right): a vector of birth-year fixed effects (λ), a vector of state fixed effects (α), the policy effect (β) where policy (MLDAXst) is a function of state and birth year, a vector of all other individual-level covariates such as demographic variables (X) and an error or disturbance term (ε).
