We obtain income tax return data from the Internal Revenue Service (IRS) Form 1040 annually. The U.S. Census Bureau aggregates this information to the state and county levels. Access to these data is vital to the health insurance coverage estimates, and these data are obtained and kept in the strictest confidentiality. No personal identifiers are included on the records used by the SAHIE program.

The summaries of the tax data that we use are:

• the number of tax exemptions by Income-to-Poverty ratio (IPR) categories, which are further divided into adult and child exemptions.
• the mean of the log of the ratio of persons' family income to their Federal Poverty Level (FPL) (a measure of the counties' general affluence);
• the variance of the log of the ratio of persons' family income to their FPL (a measure of the counties' income inequality); and

The total number of exemptions attributed to a tax return includes 1) the filer, 2) the spouse of the filer, and 3) the number of child exemptions for the household. If the adjusted gross income (AGI) on a return is below the official poverty threshold for a family of the size implied by the number of exemptions, all the exemptions (people) on the return are counted as poor (see Poverty Thresholds). AGI is not the same conceptually as family income, which the Census Bureau uses to determine official poverty status, but it is the closest proxy available.