Oregon Medicaid Lottery
Oregon Health Authority / MIT / Harvard · Oregon, USA · 2008
Summary
Oregon's random Medicaid lottery created a rare natural experiment in a domain where RCTs are normally impossible. Gaining coverage dramatically increased health care use and eliminated catastrophic medical bills, and significantly improved mental health. However, the two-year follow-up found no statistically significant improvements in blood sugar, blood pressure, or cholesterol. This null result was widely cited by ACA critics. Defenders noted that two years is too short to detect improvements in chronic disease outcomes, and that financial protection and mental health are independently valuable. The study is a masterclass in how the same data can be interpreted in opposing directions.
Research question
"What is the causal effect of gaining Medicaid coverage on health care use, financial security, and health outcomes?"
Methodology
Intervention
Oregon used a lottery to allocate limited Medicaid slots; lottery winners were randomly selected from 90,000 applicants
Assignment
Natural experiment via lottery (individual)
Sample size
~75,000 lottery participants (winners and losers), sub-studies of ~10,000
Primary outcome
Emergency room use, health care access, financial hardship, health outcomes
Effect estimate
ER use: +40%; doctor visits: +35%; financial hardship: −25% (catastrophic medical bills); depression: −30%; blood sugar, blood pressure, cholesterol: no significant improvements at 2 years
Decision
Results informed ACA debate; universal coverage advocates emphasized financial protection and mental health; skeptics emphasized null physical health outcomes at 2 years
Result
Mixed
ER use: +40%; doctor visits: +35%; financial hardship: −25% (catastrophic medical bills); depression: −30%; blood sugar, blood pressure, cholesterol: no significant improvements at 2 years
Evidence strength
Moderate
Randomized trial; replication status unknown or limited.
Replication status
N/A
Institution
Oregon Health Authority / MIT / Harvard
Location
Oregon, USA
Year
2008
Policy area
Public Health
Mechanism
Information