Factors affecting response to postal questionnaires.

Epidemiological studies of chronic diseases often use data gathered individually from many persons, rather than remaining restricted to pre-recorded data. Generally this is done by personal interview, an expensive, time-consuming procedure. The increasing educational level and social consciousness of the population suggest that a carefully designed, highly objective postal questionnaire could substitute for an interview. However, the validity of studies done this way is limited by the response rate, which tends to be lower than in interview studies. Little is known of factors affecting response to postal questionnaires and two studies were undertaken to assess some of these.