More than half of the nation’s poor and uninsured live in states that are not participating in the expansion of Medicaid, and the share among blacks is even higher.

About This Report: The analysis includes adults ages 19 to 64 and excludes people living in institutions and people who would not qualify for expanded Medicaid because of their immigration status.

The estimates of the poor and uninsured population are from the Census Bureau's 2011 American Community Survey as provided by the University of Minnesota Population Center. Poverty rates are based on the federal poverty guidelines and family definitions used in determining Medicaid eligibility and provided by the State Health Access Data Assistance Center. Immigration status was estimated based on a methodology devised by the Pew Hispanic Center.

The status of state Medicaid expansion plans is based on a report by the federal government's Center for Medicaid and CHIP Services as of Sept. 30. These lists are not finalized yet — states are still debating the issue.

The figures used are subject to some variability depending on how families are defined and the extent to which residents of group quarters are included; whether or not income is adjusted for inflation due to the rolling nature of the A.C.S. survey; the varying methods used to estimate immigration status, since the the Census Bureau only asks about citizenship, not the legal status of immigrants; and whether the A.C.S. determination of health insurance status is taken at face value. In a 2012 report, for example, researchers at the Urban Institute estimated that in addition to the poor and uninsured documented in census records, there are nearly one million Americans counted as having insurance who most likely are uninsured. However, the main findings from this analysis — that states that have chosen not to go forward with the Medicaid expansion have a higher share of the poor, uninsured population — hold up under these alternative methodological approaches and are corroborated by results obtained in other studies by the Kaiser Family Foundation and the Urban Institute.