Medicaid Increases Emergency-Department Use: Evidence from Oregon's Health Insurance Experiment

TLDR

In 2008 Oregon expanded Medicaid to low‑income adults through a lottery-based waiting list. The lottery provided a randomized design to study the effects of Medicaid coverage. The authors used the random assignment and Portland‑area emergency‑department records to follow about 25,000 participants for roughly 18 months. Medicaid coverage increased overall ED visits by 0.41 per person (40% higher than controls) and raised visits across a wide range of types, conditions, and subgroups, including those likely treatable in primary care.

Abstract

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 by using a randomized controlled design. By using the randomization provided by the lottery and emergency-department records from Portland-area hospitals, we studied the emergency department use of about 25,000 lottery participants over about 18 months after the lottery. We found that Medicaid coverage significantly increases overall emergency use by 0.41 visits per person, or 40% relative to an average of 1.02 visits per person in the control group. We found 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.