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Amanda Kowalski

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I examine treatment effect heterogeneity within an experiment to inform external validity. The local average treatment effect (LATE) gives an average treatment effect for compliers. I bound and estimate average treatment effects for always takers and never takers by extending marginal treatment effect methods. I use these methods to separate selection from treatment effect heterogeneity, generalizing the comparison of OLS to LATE. Applying these methods to the Oregon Health Insurance Experiment, I find that the treatment effect of insurance on emergency room utilization decreases from always takers to compliers to never takers. Previous utilization explains a large share of the treatment effect heterogeneity. Extrapolations show that other expansions could increase or decrease utilization.

Amanda Kowalski

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A headline result from the Oregon Health Insurance Experiment is that emergency room (ER) utilization increased. A seemingly contradictory result from the Massachusetts health reform is that ER utilization decreased. I reconcile both results by identifying treatment effect heterogeneity within the Oregon experiment and extrapolating it to Massachusetts. Even though Oregon compliers increased their ER utilization, they were adversely selected relative to Oregon never takers, who would have decreased their ER utilization. Massachusetts expanded coverage from a higher level to healthier compliers. Therefore, Massachusetts compliers are comparable to a subset of Oregon never takers, which can reconcile the results.