About the Study
The Oregon Health Insurance Experiment is a landmark, randomized study of the effect of expanding public health insurance on the health care use, health outcomes, financial strain, and well-being of low-income adults. It represents the first use of a randomized controlled design to evaluate the impact of Medicaid in the United States. Although randomized controlled trials are the gold standard in medical and scientific studies, they are rarely possible in social policy research. In 2008, the state of Oregon drew names by lottery for its Medicaid program for low-income, uninsured adults, generating just such a randomized controlled design. This ongoing study represents a collaborative effort between researchers and the state of Oregon to use this opportunity to learn about the costs and benefits of this expansion of public health insurance.
Primary Findings to Date:
About one year after the lottery, we assessed use of health care, financial strain, and self-reported health. Full results are found in: Amy Finkelstein, Sarah Taubman, Bill Wright, Mira Bernstein, Jonathan Gruber, Joseph P. Newhouse, Heidi Allen, Katherine Baicker, and the Oregon Health Study Group, "The Oregon Health Insurance Experiment: Evidence from the First Year" Quarterly Journal of Economics, 2012 Aug; 127(3): 1057-1106. We found:
Use of health care
- Medicaid increased the likelihood of being admitted to the hospital by 30 percent, driven by hospital admissions not originating in the emergency department.
- Medicaid increased the likelihood of using outpatient care by 35 percent, using prescription drugs by 15 percent, but did not seem to have an effect on use of emergency departments.
Self-reported health and well-being
- Medicaid decreased the probability of having an unpaid medical bill sent to a collection agency by 25 percent – which also benefits health care providers since the vast majority of such debts are never paid.
- Medicaid increased the probability that people report themselves in good to excellent health (compared with fair or poor health) by 25 percent.
- Medicaid increased the probability of not screening positive for depression by 10 percent.
We supplemented these data with emergency department records for an 18-month period following the lottery. Full results are found in: Sarah Taubman, Heidi Allen, Bill Wright, Katherine Baicker, Amy Finkelstein, and the Oregon Health Study Group, "Medicaid Increases Emergency Department Use: Evidence from Oregon's Health Insurance Experiment" Science, 2014 Jan 17; 343(6168): 263-268. We found:
Emergency department visits overall
Types of visits and subpopulations
- Medicaid increased the probability of using the emergency department by 7 percentage points (an increase of about 20 percent, relative to a base of 34.5 percent).
- Medicaid increased the number of emergency department visits over the 18-month period by about 40 percent (0.41 visits, relative to a base of 1.02).
- Medicaid coverage increased use of the emergency department across a broad range of types of visits and subgroups. Moreover, we did not find statistically significant decreases in emergency department use in any of the subpopulations we examine.
- Medicaid increased visits occurring during standard hours (weekdays 7am-8pm) and visits outside of standard hours (weekends and evenings). Both types of visits increased by over 40 percent (0.23 visits relative to a base of 0.57, and 0.21 visits relative to a base of 0.46, respectively).
- Medicaid increased use for visits classified as "non-emergent," "primary care treatable," and "emergent, preventable." We found no statistically significant change in the use of visits classified as "emergent, non preventable."
- Medicaid increased outpatient emergency department visits (visits that did not result in a hospital admission). We found no statistically significant increase in emergency department visits that did result in a hospital admission.
We also assessed the impact of Medicaid on labor force activity and participation in social safety net programs. Full results are found in: Baicker, Katherine, Amy Finkelstein, Jae Song, and Sarah Taubman, "The Impact of Medicaid on Labor Force Activity and Program Participation: Evidence from the Oregon Health Insurance Experiment" NBER Working Paper 19547, October 2013. We found:
Employment and earnings
- Medicaid has no statistically significant effect on employment or earnings. Our 95 percent confidence intervals allow us to reject that Medicaid causes a decline in employment of more than 4.4 percentage points, or an increase of more than 1.2 percentage points.
- Medicaid increases receipt of food stamps, but has little, if any, impact on receipt of other government benefits, including SSDI.
About two years after the lottery we conducted another survey and supplemented with objective measures of clinical health outcomes. Full results are found in: Katherine Baicker, Sarah Taubman, Heidi Allen, Mira Bernstein, Jonathan Gruber, Joseph P. Newhouse, Eric Schneider, Bill Wright, Alan Zaslavsky, Amy Finkelstein, and the Oregon Health Study Group, "The Oregon Experiment – Medicaid's Effects on Clinical Outcomes" New England Journal of Medicine, 2013 May; 368(18): 1713-1722. We found:
- Medicaid has no statistically significant effect on measured blood pressure, cholesterol or glycated hemoglobin (a measure of diabetic blood sugar control), or on the diagnosis of or medication for blood pressure or cholesterol. We can reject, with 95% confidence, increases in systolic blood pressure larger than 1.93 mm Hg and decreases larger than 2.97 mm Hg. For diastolic blood pressure, we can reject, with 95% confidence, increases larger than 1.04 mm Hg and decreases larger than 2.65 mm Hg.
- Medicaid significantly increased the probability of being diagnosed with diabetes after the lottery (by 3.8 percentage points, relative to a base rate of 1.1) and use of diabetes medication (by 5.4 percentage points, relative to a base rate of 6.4). As discussed in the paper, based on clinical trial evidence on diabetes medication, we would expect this increase in the use of medication for diabetes to decrease the average glycated hemoglobin level in the study population by 0.05 percentage points, which is well within our 95% confidence interval for the impact of Medicaid on the level of glycated hemoglobin.
- Medicaid reduced observed rates of depression by 30% (by 9.2 percentage points, relative to a base of 30).
- There was no statistically significant increase in the use of medication for depression, but Medicaid increased the probability of being diagnosed with depression after the lottery (by 3.8 percentage points, relative to a base of 4.8).
Use of health care
- Medicaid virtually eliminated out-of-pocket catastrophic medical expenditures and reduced the probability of having to borrow money or skip paying other bills because of medical expenses by more than 50%.
- Medicaid increased the use of preventive care, including an increase in cholesterol monitoring of 50 percent and a doubling of mammograms.
See publications page for more details.