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Reconciling Seemingly Contradictory Results from the Oregon Health Insurance Experiment and the Massachusetts Health Reform


  • Amanda Kowalski


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.

Suggested Citation

  • Amanda Kowalski, 2023. "Reconciling Seemingly Contradictory Results from the Oregon Health Insurance Experiment and the Massachusetts Health Reform," Artefactual Field Experiments 00774, The Field Experiments Website.
  • Handle: RePEc:feb:artefa:00774

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    Cited by:

    1. Stephen Coussens & Jann Spiess, 2021. "Improving Inference from Simple Instruments through Compliance Estimation," Papers 2108.03726,
    2. Black, Dan A. & Joo, Joonhwi & LaLonde, Robert & Smith, Jeffrey A. & Taylor, Evan J., 2022. "Simple Tests for Selection: Learning More from Instrumental Variables," Labour Economics, Elsevier, vol. 79(C).
    3. Augustine Denteh & Helge Liebert, 2022. "Who Increases Emergency Department Use? New Insights from the Oregon Health Insurance Experiment," Papers 2201.07072,, revised Apr 2023.
    4. Amanda E Kowalski, 2023. "Behaviour within a Clinical Trial and Implications for Mammography Guidelines," The Review of Economic Studies, Review of Economic Studies Ltd, vol. 90(1), pages 432-462.
    5. Pietro Emilio Spini, 2021. "Robustness, Heterogeneous Treatment Effects and Covariate Shifts," Papers 2112.09259,

    More about this item

    JEL classification:

    • C1 - Mathematical and Quantitative Methods - - Econometric and Statistical Methods and Methodology: General
    • H75 - Public Economics - - State and Local Government; Intergovernmental Relations - - - State and Local Government: Health, Education, and Welfare
    • I10 - Health, Education, and Welfare - - Health - - - General
    • I13 - Health, Education, and Welfare - - Health - - - Health Insurance, Public and Private


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