Any attempt to characterize the effects of ELE must be seen in the context of a policy that can vary widely in both its implementation and target population. This underscores the importance of assessing the effects of ELE within individual or small groups of states, as a way to best understand the ELE models that might be most effective. In order to do so, we reestimate the main model excluding one ELE state at a time to determine if the overall effect is primarily driven by the ELE experience in single state or if the ELE effect seems to vary across states.56 Similarly, we estimate state-specific models in which we define a unique set of comparison states with similar pre-ELE enrollment trends. We used the same method to select the comparison states as we did in the main model, but each model is estimated on the pre-ELE period specific to each ELE state, providing a more accurate reflection of enrollment trends before ELE implementation within that state. Although we do not place much emphasis on the individual impact estimates derived for each state, these models help validate the robustness of the main results and use a more accurate set of comparison states specific to each ELE state.
We also assess whether ELE works instantaneously or gradually by estimating a model that interacts the main ELE variable with a “number of quarters since ELE adoption” variable (set to zero for pre-ELE implementation and for non-ELE states). However, such assessments are challenging because of the limited sample of ELE states and post-implementation periods, which reduces the degrees of freedom for detecting differences between pre- and post-ELE enrollment for different ELE approaches and different post-ELE time periods.
56 The simple difference-in-difference model, which includes only state and quarter dummy variables (described in the multivariate results section) indicates that ELE states had higher enrollment growth after they implemented ELE relative to before they implemented it, compared with the changes in enrollment growth found in the non-ELE comparison states.