The Oregon Health Insurance Experiment

Last registered on April 21, 2020


Trial Information

General Information

The Oregon Health Insurance Experiment
Initial registration date
July 17, 2013

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
July 17, 2013, 8:52 PM EDT

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Last updated
April 21, 2020, 6:26 PM EDT

Last updated is the most recent time when changes to the trial's registration were published.


Primary Investigator


Other Primary Investigator(s)

PI Affiliation
PI Affiliation
National Bureau of Economic Research

Additional Trial Information

Start date
End date
Secondary IDs
The Oregon Health Insurance Experiment is a randomized evaluation of the effect of expanding access to Medicaid. In 2008, the state of Oregon drew names by lottery for its Medicaid program for low-income, uninsured adults. This ongoing study represents a collaborative effort between researchers and the state of Oregon to use this opportunity to learn about the impact of Medicaid on a variety of outcomes including health care use, health outcomes, financial strain, and well-being of low income adults.
External Link(s)

Registration Citation

Baicker, Kate, Amy Finkelstein and Sarah Taubman. 2020. "The Oregon Health Insurance Experiment." AEA RCT Registry. April 21.
Former Citation
Baicker, Kate, Amy Finkelstein and Sarah Taubman. 2020. "The Oregon Health Insurance Experiment." AEA RCT Registry. April 21.
Sponsors & Partners

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Experimental Details


Treatment group: 29,834 people and 24,912 households selected in the lottery (the lottery winners)
Control group: 45,088 and 41,473 households not selected (the control group).

Adults randomly selected in the lottery were given the option to apply for Medicaid (specifically Oregon Health Plan Standard).Oregon Health Plan Standard provides comprehensive medical benefits, including prescription drugs, with no patient cost-sharing and low monthly premiums ($0 to $20, based on income), mostly through managed-care organizations.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
health care use, health, financial strain
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
In early 2008, Oregon opened a waiting list for its Medicaid program for low-income adults that had previously been closed to new enrollment. Approximately 90,000 people signed up for the available 10,000 openings. The state drew names from this waiting list by lottery to fill the openings. Persons who were selected won the opportunity — for themselves and any household member — to apply for Oregon Health Plan Standard and were sent an application. Those who sent back their application and met eligibility requirements were enrolled in Oregon Health Plan Standard. This random selection allows researchers to gauge the causal effects of Medicaid. The study compiles rich data from many sources to examine a wide range of potential effects of insurance. Data include mail surveys, in-person interviews and health exams, and administrative data such as hospital records.
Experimental Design Details
Randomization Method
In 2008, the state of Oregon drew names by lottery. Randomization was done on state computer.
Randomization Unit
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
66,385 households
Sample size: planned number of observations
74,922 people
Sample size (or number of clusters) by treatment arms
Treatment= 29,834 people and 24,912 households Control= 45,088 people and 41,473 households.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Supporting Documents and Materials

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Institutional Review Boards (IRBs)

IRB Name
Massachusetts Institute of Technology
IRB Approval Date
IRB Approval Number
IRB Name
IRB Approval Date
IRB Approval Number
OHRA P17925
IRB Name
Providence: mail survey
IRB Approval Date
IRB Approval Number
IRB Name
Providence: admin and in-person
IRB Approval Date
IRB Approval Number
IRB Name
IRB Approval Date
IRB Approval Number
FWA 3692
IRB Name
Portland State University
IRB Approval Date
IRB Approval Number
HSRRC 08501
Analysis Plan

Analysis Plan Documents

Neighborhood Characteristics Analysis Plan - 2020-04-21

MD5: 6245b0b16231621de16c51459684e740

SHA1: 5aee58a13bb5b6c7c4d44c3894e942d3a0868b71

Uploaded At: April 21, 2020

The Short-Run Impact of Extending Public Health Insurance to Low-Income Adults: Evidence from the First Year of The Oregon Medicaid Experiment - Analysis Plan 2010-12-01

MD5: 8d9b0fe0e83fef437f33e7bec4170e7d

SHA1: 960f8770229e0fa858bc8ac465e69eb837ffbf85

Uploaded At: November 08, 2013

Dental Care Analysis Plan - 2014-11-17

MD5: 7ded64780f996ffa762b03ed314f7603

SHA1: 757e385b8f21e2058826d3c2ee353ed04d54821f

Uploaded At: November 21, 2014

Depression and the Impact of Medicaid Analysis Plan - 2014-12-15

MD5: 54df9f21003bb78d86ab6c3ff68f9de4

SHA1: 26c0031abf2c426480432a1cb112af0d661f5255

Uploaded At: December 15, 2014

Criminal Charges Analysis Plan - 2014-04-30

MD5: 61c7fae83e12b51595126749e42c242f

SHA1: 93167c501ed289fae6d43df05218803168b2bf89

Uploaded At: April 30, 2014

Evidence from the In-person Interviews Analysis Plan - 2012-04-16

MD5: 811f57175cd6243f7922d8d451dc6087

SHA1: b8998771bf861904b5eb7a97575e48956673654b

Uploaded At: November 08, 2013

Evidence from Emergency Department Data Analysis Plan - 2013-03-06

MD5: a525344271955567c734e7ba72d198bb

SHA1: c3e56f6fbc13f441ea4d51d0276a2dc1aca4d75b

Uploaded At: November 08, 2013

Effect on Medications Analysis Plan - 2015-07-15

MD5: 6d399106c3c854aa1b3df85cda6ab3fb

SHA1: ed61bfa0feba8478eedd4fd53d5a520357d1af0f

Uploaded At: July 15, 2015

Evidence From Voting Data Analysis Plan - 2015-09-23

MD5: bb42d1f9e93dfeb05adc78f779e5d6d2

SHA1: 6d3a79d0473fd221abaaa56c1dcab858538b6f83

Uploaded At: September 24, 2015

Effect on Disease Management Analysis Plan - 2019-04-05

MD5: 84b600fc3ffb1c6e581372bbbcf7805f

SHA1: 3600ec1d8fc93c481237aa520f5d0c45c9e6d549

Uploaded At: April 05, 2019


Post Trial Information

Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
December 31, 2013, 12:00 +00:00
Data Collection Complete
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

In 2008, Oregon initiated a limited expansion of a Medicaid program for uninsured, low-income adults, drawing names from a waiting list by lottery. This lottery created a rare opportunity to study the effects of Medicaid coverage using a randomized controlled design. Using the randomization provided by the lottery and emergency department records from Portland-area hospitals, we study the emergency department use of about 25,000 lottery participants over approximately 18 months after the lottery. We find that Medicaid coverage significantly increases overall emergency use by 0.41 visits per person, or 40 percent relative to an average of 1.02 visits per person in the control group. We find increases in emergency department visits across a broad range of types of visits, conditions, and subgroups, including increases in visits for conditions that may be most readily treatable in primary care settings.
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.
In 2008, a group of uninsured low-income adults in Oregon was selected by lottery for the chance to apply for Medicaid. We use this randomized design and 2009 administrative data to evaluate the effect of Medicaid on labor market outcomes and participation in other social safety net programs. We find no significant effect of Medicaid 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. We find that Medicaid increases receipt of food stamps, but has little, if any, impact on receipt of other government benefits, including SSDI.
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.
Despite imminent expansion of Medicaid to low-income adults, the effects of expanding coverage are unclear. Oregon’s 2008 Medicaid expansion using lottery drawings from a waiting list provides an opportunity to evaluate the effects of Medicaid using random assignment. Approximately two years after the lottery, we collected data from 6,387 adults randomly selected to be able to apply for Medicaid coverage and 5,842 not selected. Measures included blood pressure, cholesterol and glycosylated hemoglobin; a depression screen; medication catalogs; and self-reported diagnoses, health, health care utilization and out-of-pocket spending. We use the lottery’s random assignment to calculate the effect of Medicaid coverage.We found no statistically significant effect of Medicaid on the prevalence, diagnosis, or medication of hypertension or high cholesterol. Medicaid coverage significantly increased the diagnosis of diabetes and use of diabetes medication, but we observed no significant effect on average glycosylated hemoglobin levels nor on the percent with levels >6.5%. Medicaid coverage decreased the probability of screening positive for depression (-9.15 percentage points; 95% CI: -16.70 to -1.60; P=0.018), increased use of preventive services, and almost eliminated catastrophic out-of-pocket medical expenditures. Thus, evidence using a randomized controlled design showed that Medicaid coverage generated no statistically significant improvements in measured physical health outcomes in the first two years, but did generate increased health care use, higher rates of diabetes detection and management, lower rates of depression, and lower financial strain.
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 – Effects of Medicaid on Clinical Outcomes" New England Journal of Medicine, 2013 May; 368(18): 1713-1722.
In 2008, a group of uninsured low-income adults in Oregon was selected by lottery to be given the chance to apply for Medicaid. This lottery provides an opportunity to gauge the effects of expanding access to public health insurance on the health care use, financial strain, and health of low-income adults using a randomized controlled design. In the year after random assignment, the treatment group selected by the lottery was about 25 percentage points more likely to have insurance than the control group that was not selected. We find that in this first year, the treatment group had substantively and statistically significantly higher health care utilization (including primary and preventive care as well as hospitalizations), lower out-of-pocket medical expenditures and medical debt (including fewer bills sent to collection), and better self-reported physical and mental health than the control group.
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.

Reports & Other Materials