Sociodemographic variables for general practices: use of census data

Measures of the social, ethnic, and demographic characteristics of general practice populations are essential both for planning health services and for research. Such measures can be derived by combining census data for electoral wards with postcoded data from a family health services authority's age-sex register.1 Because electoral wards have large populations (typically 5000-15000 people), the patients registered with individual general practices will rarely be representative of a ward, and this will reduce the accuracy of census derived variables. Enumeration districts, however, have smaller populations (typically 200-600 people). We (a) derived estimates of age structure of practice populations based on enumeration districts and electoral wards and compared them with those obtained from the authority's age-sex registry and (b) compared the predictive power of variables derived from enumeration districts and electoral wards in explaining the variation in breast cancer screening rates among these practices. The family health services authority provided a database …