METHODOLOGY

To determine the states where the Affordable Care Act (ACA) has improved health insurance coverage the most, 24/7 Wall St. ranked states on the largest percentage point decline in uninsured rates from 2012 through 2015. Each year, the U.S. Census Bureau’s American Community Survey (ACS) calculates the proportion of the noninstitutional population that does not have health insurance. The noninstitutional population excludes those in prisons, retirement homes, mental facilities, or on active duty with the Armed Forces.

We used data from the Department of Health and Human Services (HHS) on the number of people in each state who are covered by an insurance plan as of March 2015 through a state or federal exchange. Also from the HHS, we included the number of people who have gained Medicaid coverage since the rollout of the ACA in October 2013. Even in states that did not approve of the Medicaid expansion as part of the ACA implementation, Medicaid coverage changed as people’s incomes fell below the federal poverty level.

To calculate the number of people who gained insurance since the rollout, we added the number of people who enrolled in a marketplace plan for 2015 and the number of people who gained Medicaid coverage since the beginning of the ACA implementation. To avoid significant overestimates due to double counting, we adjusted our 2015 insured population by about 26% to arrive at a net increase in health insurance coverage of roughly 17 million people nationwide. This figure is consistent with other estimates.

The uninsured population in 2015 was calculated by subtracting the insured population in 2015 from the uninsured population in 2012. Next, we projected growth in each state’s noninstitutional population for 2014 and 2015 in two rounds and used it to find the share of each state’s population that does not have insurance this year.

In many cases, Medicaid expansion had a significant impact on the decline of a state’s uninsured population. Whether or not a state expanded Medicaid came from the Kaiser Family Foundation, which reviewed each state’s health system in July 2015. For the state’s that did not expand Medicaid, the HHS provided estimates of the number of people who would become eligible for coverage if the state opts for expansion. In addition to our estimates of health insurance coverage, we also calculated what the uninsured rate would be if the state opted to expand Medicaid.

Additionally, we considered annual unemployment rates from 2011 through April 2015 from the Bureau of Labor Statistics. From the ACS, we reviewed the share of households earning less than $10,000 each year and the share of households earning more than $200,000. We also reviewed median household income, poverty rates, educational attainment rates, and the percentage of the population that received food stamps. All ACS data are for 2013, the most recent period for which data are available.