Table 1.

Variables Used in Multilevel Regression Analysis

Characteristic of Sample Population	Data Source
Enabling/Disabling	Developed from CMS Medicare 100% Denominator Files, 2001-2005, and calculations performed using geocoded data and distance algorithms
Moved to a new ZIP code in same state, 2001-2005
Months with extra assistance from state Medicaid to purchase Part B insurance, 2001-2005
Distance (miles) to closest endoscopy facility
Predisposing
Age in 2001
Gender; race or ethnicity
Socio-Demographic Factors (PCSA area)
Social Integration and Support: Segregation (isolation) index describing residential segregation by race or ethnicity, following Massey and Denton [52]	Developed from US Census 2000 data at ZCTA levels aggregated to PCSAs using ZCTA-PCSA crosswalk: http://rtispatialdata.rti.org
Stressor, Driver Courtesy: Commuter intensity reflecting the proportion of the workforce commuting 60 minutes or more each way to work
Social or Cultural Cohesion: Proportion of the population aged 65+ with little or no English language ability, 2000
Health System Factors (County area)
Capacity: Average number of endoscopy facilities per thousand population aged 65+ in each person's residential area, defined in 2001	Providers identified from CMS Medicare outpatient claims files; annual census population
Capacity: Number of oncologists or per thousand population aged 65+, defined in 2001	Area Resource File and annual census population
Market factor: MMC plan penetration, defined in 1998	CMS Geographic Service Area File
Market stressors: Proportion of population living below the federal poverty level in 2001; proportion of the county that is rural	Census annual poverty and population

Note: MMC = Medicare managed care; ZCTA = ZIP Code Tabulation Area; HRSA = Health Resources and Services Administration; PCSA = Primary Care Service Area; CMS = Centers for Medicare & Medicaid Services.