Random digit dialling and Electronic White Pages samples compared: demographic profiles and health estimates

Objective: To compare the methodologies of and health estimates derived fro m two telephone household survey methods. In particular, to establish if Wh ite Pages telephone listings provide a relatively unbiased sampling frame f or population health surveys. Method: In South Australia in 1998, a health survey questionnaire was admin istered by telephone to two randomly selected population samples. The first method used EWP (Electronic White Pages, n=6,012), which contains ail list ed residential telephone numbers as the sampling frame. The results were co mpared to a RDD (random digit dialling, n=3,080) sample where all listed an d unlisted telephone numbers were included in the sampling frame. Demograph ic variables and health estimates were compared between the surveys, and th en compared to a 'gold standard' door-to-door household survey conducted co ncurrently. Results: The response rate for EWP (83.8%) exceeded that of RDD (65.4%). Mo re than four times as many calls were required per completed interview in R DD. Demographic profiles and health estimates were substantially similar. Conclusions: EWP requires fewer telephone calls and enables approach letter s establishing the bona fides of the survey to be sent to each selected add ress before calling, increasing the response rate. RDD is a more inclusive sampling frame but also includes nonconnected and business numbers, and off ers no significant advantages in providing health estimates. Implications: There are substantial methodological and cost advantages in u sing EWP over RDD as the sampling frame for population health surveys, with out introducing significant bias into health estimates.