The Oregon Health Study

Not since the RAND Health Insurance Experiment (HIE) has there been a randomized controlled experiment of the effect of insurance on health outcomes. Finally, a second one is underway, the Oregon Health Study (OHS). It’s being conducted by Heidi Allen, Katherine Baicker, Amy Finkelstein, Sarah Taubman, Bill J. Wright, and the Oregon Health Study Group who report on the study design in the most recent edition of Health Affairs.

[T]he Oregon Health Study [is] a randomized controlled trial that will be able to shed some light on the likely effects of [Medicaid] expansions. In 2008, Oregon randomly drew names from a waiting list for its previously closed public insurance program. Our analysis of enrollment into this program found that people who signed up for the waiting list and enrolled in the Oregon Medicaid program were likely to have worse health than those who did not. However, actual enrollment was fairly low, partly because many applicants did not meet eligibility standards.

Get excited! But don’t get too excited. The study runs through 2010 and no outcome results are available yet.

The paper includes a nice summary of observational, quasi-experimental, and experimental studies of the effects of public insurance programs on outcomes. As I’ve written before, observational studies are not of primary interest to me. There’s only been one other experimental study (RAND HIE). About the quasi-experimental studies, the authors write,

Some studies have found evidence that public health insurance reduces mortality among infants and children [8-10] and improves some outcomes—although not mortality—among the elderly. [11–14] Although they are much more persuasive than observational studies, quasi-experimental studies are not truly randomized. Thus, investigators must rely on the assumption that the people whose health insurance was affected by environmental or policy changes are otherwise identical to the people in the comparison group.

The authors’ references 8-14 are listed below. References 8 and 9 pertain to Medicaid and are on my list of papers as part of the “Medicaid-IV” project.


8. Currie J, Gruber J. Saving babies: the efficacy and cost of recent expansions of Medicaid eligibility for pregnant women. J Polit Econ. 1996;104(6):1263–96.

9. Currie J, Gruber J. Health insurance eligibility, utilization of medical care, and child health. Q J Econ. 1996;111(2):431–66.

10. Hanratty MJ. Canadian national health insurance and infant health. Am Econ Rev. 1996;86(1):276–84.

11. Card D, Dobkin C, Maestas N. The impact of nearly universal health care coverage on health care utilization: evidence from Medicare. Am Econ Rev. Forthcoming.

12. McWilliams JM, Meara E, Zaslavsky AM, Ayanian JZ. Health of previously uninsured adults after acquiring Medicare coverage. JAMA. 2007; 298(24):2886–94.

13. McWilliams JM, Meara E, Zaslavsky A, Ayanian JZ. Use of health services by previously uninsured Medicare beneficiaries. New Engl J Med. 2007; 357(2):143–53.

14. Finkelstein A, McKnight R.What did Medicare do? The initial impact of Medicare on mortality and out of pocket medical spending. J Public Econ. 2008;92(7):1644–69.

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