Use of medicare claims data to estimate national trends in stroke incidence, 1985-1991

Although stroke mortality has been declining in the United States for decades, recent trends in stroke incidence based on national data have not been described. We used Medicare hospitalization data to estimate national trends in the incidence of stroke among Americans aged 70 years or older, and we provide evidence of the validity of the estimate. We defined stroke as a principal diagnosis with International Classification of Diseases, 9th Revision, Clinical Modification codes 430 to 434 or 436 to 437. We excluded many recurrent cases from the analysis by eliminating persons hospitalized for stroke during the 5 years preceding the index stroke. We calculated annual adjusted incidence rates and examined trends graphically. We investigated the effect of different exclusion periods, trends in in-hospital mortality of stroke patients, and trends in out-of-hospital stroke mortality. We examined trends in relation to sex, race, and age. 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 diagnosis 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 blacks. Stroke incidence declined steadily from 1985 to 1989 and then increased slightly to 1991. Several postulated potential sources of bias were investigated and found to be unlikely to account for the incidence decline, although some may have contributed to the subsequent incidence increase.