From Pages to Practice

Published March 8, 2017


The Affordable Care Act (ACA) initially required states to expand Medicaid programs to cover Americans in households with incomes below 138% of the federal poverty level. However, the U.S. Supreme Court deemed the mandate unconstitutional, making Medicaid expansion optional for states. Allowing states to opt-out of Medicaid expansion has created a natural experiment to measure the impact of Medicaid on health coverage and outcomes. As the U.S. enters a time of great uncertainty about the future of our health care system, it is critical to understand how policies implemented during the last several years have affected health and health care in this country.

In this week’s issue of NEJM, researchers used data from the National Health Interview Survey (NHIS) to examine the effect of Medicaid expansion on health care coverage, access, utilization, and outcomes in 60,766 adults with incomes below 138% of the federal poverty level. Using a difference-in-differences design, the researchers compared changes in outcomes in states with and without Medicaid expansion during the four years before the expansion (2010–2013) and the two years after (2014–2015)  

The first group of outcomes measured changes in health care coverage and utilization of health care services. As expected, Medicaid coverage increased significantly more during the two years after expansion in expansion states than in non-expansion states, with a larger increase in the second year (difference-in-differences, 15.6 percentage points; P<0.001). Reports of overnight hospital stays increased more in expansion states during year 1 but not year 2; rates of cholesterol testing increased compared with the preexpansion period. No changes were noted between states with and without expansion in visits to health care providers, blood pressure checks, influenza vaccinations, or cancer screening.

The second category of outcomes measured access to care. Patients in expansion states were less likely to report being unable to afford necessary follow-up care (-3.4 percentage points, P=0.002) and less likely to worry about their ability to pay bills. However, patients in expansion states were more likely to report delaying care due to appointment availability or wait times.

The third category of outcomes analyzed health status. Patients in expansion states reported an increased incidence of diagnoses of diabetes, high cholesterol, and depression in the first year after expansion but this difference disappeared in the second year.

This study provides an important analysis of the impact of Medicaid expansion. The results are limited by the inherent shortcomings of a natural experiment.  The data imply a backlog of health services, leading to more hospitalizations and diagnoses of chronic illnesses in the first year after expansion. Although the expansion of Medicaid coverage has reduced patient reports of being unable to afford care, reports of delayed care due to appointment wait times suggest that availability of health care services has not caught up with the increased demand created by Medicaid expansion.

As policymakers debate the next steps for the future of health care in America, data such as these should serve as a foundation for decisions about coverage, access, quality, and cost. Health care may be complicated, but patients with limited resources deserve access to high-quality health care under our safety-net system.

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Rebecca Berger, MD
Rebecca is a 2016-2017 NEJM Editorial Fellow and a hospitalist at Massachusetts General Hospital. She graduated from Columbia University College of Physicians and Surgeons in 2013 and completed internal medicine residency at Massachusetts General Hospital in 2016. Her interests include medical education, quality improvement, patient safety, health care delivery innovation, and teaching value in health care.