Book excerpt: The Social Security Administration (SSA) administers two programs that provide benefits based on disability: the Social Security Disability Insurance (SSDI) program and the Supplemental Security Income (SSI) program. This report analyzes health care utilizations as they relate to impairment severity and SSA's definition of disability. Health Care Utilization as a Proxy in Disability Determination identifies types of utilizations that might be good proxies for "listing-level" severity; that is, what represents an impairment, or combination of impairments, that are severe enough to prevent a person from doing any gainful activity, regardless of age, education, or work experience.