Table 1.

Data Sources Used in the Study

Data system*	Description	Years included	Population
Nationwide Centers for Medicaid and Medicare Services, Medicaid data, including Medicare data for those dual-eligible for Medicaid and Medicare (MAX)	Dual-eligible adults with Medicaid and Medicare, and adults/children with Medicaid only (excluding Tennessee)	2000–2006	1.7 million**
Tennessee Medicaid eligible plus other TennCare enrollees	Low income state-run health plan in Tennessee	1998–2007	1.2 million
New Jersey PAAD and Pennsylvania PACE	Low-income elderly not eligible for Medicaid receiving prescription assistance.	1998–2006	480,000
Kaiser Permanente Northern California (KPNC)	Health-plan members	1998–2007	3.2 million

^*Nationwide Centers for Medicaid and Medicare Services files: Medicaid-only and Medicaid/Medicare dual eligible patients linked nationwide data files, including Medicaid Analytic eXtract (MAX) files and Medicare claims files (part D prescription drug files available for 2006 only). Tenncare: Patients enrolled in Tenncare, an enhancement to the state Medicaid program, augmented by existing linkages to a wide range of Tennessee state data. PAAD: Pharmaceutical Assistance to the Aged and Disabled (New Jersey). PACE: Pharmaceutical Assistance Contract for the Elderly (Pennsylvania).

^**Approximately 16% of the U.S. population is currently covered by Medicaid in 2008–2009 (http://www.statehealthfacts.org/mfs.jsp?rgn=6&rgn=1). The MAX data used in the present study comprised only those patients with one of the autoimmune diseases under study during the period 2000–2006.