USE OF MEDICARE CLAIMS DATA TO ESTIMATE NATIONAL TRENDS IN STROKE INCIDENCE, 1985-1991

Background and Purpose Although stroke mortality has been declining in the United States for decades, recent trends in stroke incidence base d on national data have not been described. We used Medicare hospitali zation data to estimate national trends in the incidence of stroke amo ng Americans aged 70 years or older, and we provide evidence of the va lidity of the estimate. Methods We defined stroke as a principal diagn osis with International Classification of Diseases, 9th Revision, Clin ical Modification codes 430 to 434 or 436 to 437. We excluded many rec urrent cases from the analysis by eliminating persons hospitalized for stroke during the 5 years preceding the index stroke. We calculated a nnual adjusted incidence rates and examined trends graphically. We inv estigated the effect of different exclusion periods, trends in in-hosp ital mortality of stroke patients, and trends in out-of-hospital strok e mortality. We examined trends in relation to sex, race, and age. Res ults The estimated age- and sex-adjusted stroke incidence declined 9.5 % from 1985 to 1989, then increased 3.3% to 1991. The pattern did not vary with the length of the exclusion period or when all listed diagno ses rather than principal diagnoses were used to identify stroke cases . Incidence trends resembled the overall trend for both men and women. for 5-year age groups, and for whites; the trend did not change for b lacks. Conclusions Stroke incidence declined steadily from 1985 to 198 9 and then increased slightly to 1991. Several postulated potential so urces of bias were investigated and found to be unlikely to account fo r the incidence decline, although some may have contributed to the sub sequent incidence increase.