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, Vol. 127, Issue 3. August 2012. 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.
       
• Financial hardship
  • 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.
  
• Self-reported health and well-being
  • 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.
  

About two years after the lottery we updated these data 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, Volume 368, Issue 18. May 2013. We found:

• Physical health
  • Medicaid has no statistically significant effect on measured blood pressure, cholesterol or HbA1c (a measure of diabetic blood sugar control), or on the diagnosis of or medication for blood pressure or cholesterol.
  • 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).
       
• Mental health
  • 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).
• Financial hardship
  • 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%.
  
• Use of health care
  • 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