USE OF MEDICARE CLAIMS DATA TO MEASURE COUNTY-LEVEL VARIATIONS IN THEINCIDENCE OF COLORECTAL-CARCINOMA

BACKGROUND, Population-based cancer registries that can be used to com pare cancer incidence and mortality across regions of the U.S. are cur rently lacking. The authors conducted this study to validate Medicare claims as a measure of county-level colorectal carcinoma incidence amo ng older Americans. Variations found among counties are described in t his article. METHODS. A total of 183,174 hospitalized patients age 65 years in 1991-1993 with newly diagnosed colorectal carcinoma who resid ed in one of 480 large counties were identified in Medicare files. The county-level truncated age, race, and gender adjusted incidence rates for the population age 65 years, the proportion of patients with a co de indicating distant metastases, and the 2-year case-fatality rates w ere determined. Corresponding rates from the SEER database were compar ed. RESULTS. The median truncated adjusted 3-year incidence rate was 8 70 per 100,000 (Quartile 1-Quartile 3, 779-955), with almost twofold d ifferences among counties even after the exclusion of outliers. The me dian proportion of patients with codes indicating distant metastases w as 23.4% (range, 10.2-46.9%; Quartile l-Quartile 3, 20.8-25.8), and th e average 2-year case-fatality rate was 39.2% (range, 26.5-51.4%; Quar tile l-Quartile 3, 37.0-41.6). Medicare files tended to underestimate the truncated incidence rate according to SEER, but among counties the two sets of rates were closely correlated (r = 0.94, P < 0.0001). CON CLUSIONS. Medicare files are a potential alternative source of nationa l data for the study of colorectal carcinoma incidence among the elder ly at the county level. The data also suggest significant variations a mong counties in colorectal carcinoma incidence, stage, and mortality that could be used in public health initiatives. Cancer 1998;83:673-8. (C) 1998 American Cancer Society.