SELECTION BIAS FROM SAMPLING FRAMES - TELEPHONE DIRECTORY AND ELECTORAL ROLL COMPARED WITH DOOR-TO-DOOR POPULATION CENSUS - RESULTS FROM THE BLUE MOUNTAINS EYE STUDY

Many Australian public health research studies use the telephone direc tory or the electoral roll as a sampling frame from which to draw stud y subjects. The sociodemographic, disease-state and risk-factor charac teristics of subjects who could be recruited using only the telephone directory or only the electoral roll sampling frames were compared wit h the characteristics of subjects who would have been missed using onl y these sampling frames, respectively. In the first phase of the Blue Mountains Eye Study we interviewed and examined 2557 people aged 49 an d over living in a defined postcode area, recruited from a door-to-doo r census. This represented a participation rate of 80.9 per cent and a response rate of 87.9 per cent. The telephone directory was searched for each subject's telephone number and the electoral roll was searche d for each subject. Subject characteristics for those who were present in each of these sampling frames were compared with the characteristi cs of those subjects not included in the sampling frames. The telephon e directory listed 2102 (82.2 per cent) of the subjects, and 115 (4.5 per cent) had no telephone connected. The electoral roll contained 215 6 (84.3 per cent) of the subjects, and 141 subjects (5.5 per cent) cou ld not be found in either the electoral roll or the telephone director y. Younger subjects, subjects who did not own their own homes and subj ects born outside of Australia were significantly less likely to be in cluded in either of these sampling frames. The telephone directory was also more likely to exclude subjects with higher occupational prestig e, while the electoral roll was more likely to exclude unmarried perso ns and males. Researchers using the telephone directory and electoral roll to select subjects for study should be aware of the potential sel ection bias these sampling frames incur and need to take care when gen eralising their findings to the wider community.