State variation in the characteristics of Medicare-Medicaid dual enrollees: Implications for risk adjustment.

Objective: To examine between-state differences in the socioeconomic and health characteristics of Medicare beneficiaries dually enrolled in Medicaid, focusing on characteristics not observable to or used by policy makers for risk adjustment.

Data Source: 2010-2013 Medicare Current Beneficiary Survey.

Study Design: Retrospective analyses of survey-reported health and socioeconomic status (SES) measures among low-income Medicare beneficiaries and low-income dual enrollees. We used hierarchical linear regression models with state random effects to estimate the between-state variation in respondent characteristics and linear models to compare the characteristics of dual enrollees by state Medicaid policies.

Principal Findings: Between-state differences in health and socioeconomic risk among low-income Medicare beneficiaries, as measured by the coefficient of variation, ranged from 17.5 percent for an index of socioeconomic risk to 20.3 percent for an index of health risk. Between-state differences were comparable among the subset of low-income beneficiaries dually enrolled in Medicare and Medicaid. Dual enrollees with incomes below the Federal Poverty Level were in better health and had higher SES in states that offered Medicaid to individuals with relatively higher incomes. Duals' average incomes were higher in states with Medically Needy programs.

Conclusions: Characteristics of dual enrollees differ substantially across states, reflecting differences in states' low-income Medicare populations and Medicaid policies. Risk-adjustment methods using dual enrollment to proxy for poor health and low SES should account for this state-level heterogeneity.