It is unknown whether major changes in population insurance coverage are associated with changes in thirty‐day hospital readmission rates, despite the Affordable Care Act’s coverage expansions coming into effect this year.


To evaluate the impact of a large‐scale insurance expansion on hospital readmission rates, using Massachusetts’ 2006 health insurance expansion as a natural experiment.


We used a difference‐in‐differences quasi‐experimental design that incorporated data from 2004‐2010, two years before and after the 2006‐2008 Massachusetts insurance expansion.

Claims databases from the Massachusetts government were obtained, consisting of all patient admissions to all MA hospitals reported on a quarterly basis for the fiscal year. Hospitals were stratified into quartiles based on the pre‐reform insurance status of their patient populations. Patients 65 years or older and those younger than 18 years were excluded to focus on the demographic that benefited most from Massachusetts’ insurance expansion.

Decreases in uninsurance rates during and after reform were largely limited to the hospital quartile with the highest pre‐reform uninsurance rates (from 14% uninsured at the start of the reform to 2.9% by the end of the study period; Figure 1). The other hospital quartiles collectively experienced only a minor decline in their percentage of uninsured admissions (5.9% at the start of reform to 2.5% by the end of the study period). According to difference‐in‐differences regression analysis, the highest uninsured hospital quartile experienced a modest increase in their readmissions rate of 0.6% (95% CI of 0.1%‐1.1%) during the reform period as compared to the other three hospital quartiles (p=0.01; Figure 2).


The insurance expansions of the Affordable Care Act are similar in time frame and mechanism but greater in magnitude than the Massachusetts law. Thus, the Massachusetts experience suggests that as the country goes through ACA’s major insurance expansion, facilities that cared disproportionately for uninsured patients prior to the expansion may similarly experience increases in readmissions.

Figure 1

Figure 2