Definition of Population at Risk
Since the nonelderly population comprises 93% of the asthma population nationwide, this asthma hospitalization analysis was restricted to California residents <64 years. Information on hospitalizations was obtained from the 1993 California Hospital Discharge file, maintained by the California Office of Statewide Health Planning and Development. This data set represents all of the 3.7 million discharges from acute care nonfederal general hospitals in California in 1993. Information used from this file includes patient age, sex, race/ethnicity (white, black, Hispanic, Asian, Native American/Eskimo, other, and unknown), residence zip code, hospital length of stay in days, source of admission, source of payment, and principal diagnosis. All hospital discharges for California residents in calendar year 1993 with a three-digit International Classification of Diseases, Ninth Revision-Clinical Modification (ICD-9-CM) primary medical diagnosis code of 493, asthma, were selected. canadian drug mall

Information on area population characteristics by three-digit zip code in California (eg, each area s population by age, sex, and race/ethnicity, median household income, percentage of the population that were black, Hispanic, and Asian, and urbanicity) was derived from the 1990 US Bureau of the Census Summary Tape File 3B. Data from the 1990 US Bureau of the Census Summary Tape File 3B was matched to the three-digit zip code of the residence of each inpatient reported in the 1993 California Hospital Discharge file. Information on median household income was obtained from the 1990 US Bureau of the Census data because patient-level income data were not available in the 1993 California Hospital Discharge file. The number of persons ^65 years residing in the three-digit zip code areas ranged from 35,939 (which includes portions of Sacramento, El Dorado, and Placer counties) to 2.1 million (which includes a portion of Los Angeles county). A three-digit zip code area was classified as rural if >20% of its population resided in rural farm or nonfarm areas; otherwise, the three-digit zip code area was classified as urban.