Individuals eligible for Supplemental Security Income (SSI) benefits are eligible for Medicaid, a staterun program providing health insurance to people with low-income, and with low income and disabilities. Individuals eligible for both SSI and Social Security Disability Income (DI) receive primary coverage from Medicare, a federally-run program providing health insurance at older ages, and to DI beneficiaries, with Medicaid providing supplemental coverage. Despite the importance of these two programs for the health care system and for adults and children with disabilities in particular, there is little evidence on how they differ in
their effects on beneficiaries. We use a novel strategy to estimate the causal effect of enrolling an SSI beneficiary in Medicaid vs. Medicare. Specifically, we use a difference-in-differences design to compare changes in spending, health, and earnings at age 65 for a treatment group of individuals enrolled in SSI only (and thus Medicaid but not Medicare) at age 63 and a control group of individuals enrolled in both SSI and DI (and thus Medicare with Medicaid supplemental coverage) at age 63. At age 65, the treatment group switches from Medicaid-only to Medicare with supplemental Medicaid, while the control group experiences no change. This strategy will allow us to estimate differences in outcomes between Medicaid and Medicare coverage for the same person. Our results will shed light on a previously unanswered question: How would outcomes be different for SSI beneficiaries if they were enrolled in Medicare instead of Medicaid? This will help inform state policy and SSA policy for adults with disabilities.