Limitations and potential uses of census-based data on ethnicity in a diverse community

Purpose Information on ethnicity, socioeconomic status, and social class has value in epidemiologic research and in measurement of the quality of health care but it is difficult to obtain for large populations. This evaluation assessed the potential usefulness of ethnicity data based on address geocoding to the 2000 census. Methods We compared ethnicity based on the geocoding data with ethnicity from hospitalization records and birth certificates of a large health maintenance organization. Results Of 117,209 members with black ethnicity recorded at the time of a hospitalization, the mean percentage of blacks in their geocoded block was only 37%. Among the 62,661 individuals recorded as Asian at the time of a hospitalization, the mean percentage of Asians in their geocoded block was only 24%. Among the 47,328 individuals who lived in a census block that had 50% or more blacks, 81% were recorded as black at the time of a hospitalization. Among the 24,424 individuals who lived in a census block that had 50% or more Asians, 38% were recorded as being Asian at the time of a hospitalization. Conclusions In our population, information on ethnicity derived from geocoding at the block level cannot be used to infer the ethnicity of Asian or black individuals.