Why did the SSI-disabled program grow so much? Disentangling the effect of Medicaid

The participation rate for working-age adults in the Supplemental Security Income (SSI) program increased by 37 percent from 1987 to 1993. This paper examines the role of public health insurance provided through Medicaid on the SSI participation decision. I use the rapid growth in Medicaid expenditure across states and over time as a proxy for its value. The estimation is complicated by the easing of standards for determining disability. If the marginal individual who entered SSI under these easier standards was healthier than the average participant, then average Medicaid expenditure would fall. Thus, conventional OLS estimates could lead to a spurious negative correlation between average Medicaid expenditure and SSI participation. I therefore apply two-stage least squares (TSLS) to estimate Medicaid's effect, using Medicaid expenditure for blind and elderly SSI recipients, and adult and child AFDC recipients as instruments for disabled Medicaid expenditure. <p>The TSLS estimates indicate that rising Medicaid expenditure significantly increased the SSI participation for whites, but had little effect on African Americans. Among whites, the rising value of Medicaid explains one-third of the growth in SSI participation.