Mode of delivery, but not questionnaire length, affected response in an epidemiological study of eating-disordered behavior

The effects of questionnaire length and mode of delivery on response rates were examined in an epidemiological study of eating-disordered behavior. Short (8 pages) and long (14 pages) questionnaires were posted or hand-delivered to a community sample of 802 women. Nonrespondents who received the first questionnaire by hand delivery received a reminder letter and replacement questionnaire by post; those who received the initial questionnaire by post were further randomized to receive the first reminder by hand delivery or by post, in short or long form. A second reminder letter and questionnaire (in short or long form) were posted to all remaining nonrespondents. The overall response rate was 52.9%. This is a conservative estimate of true response, because in a substantial proportion of cases (12.2%) individuals were no longer resident at the listed address. There was a significant effect of mode of delivery on response, favoring hand delivery, at both the initial mailout and first reminder. There was no effect of questionnaire length on response to the initial mailout, although overall response was significantly higher for the longer form. It was estimated that an overall response of 58.0% would have been achieved had first reminders been hand-delivered to all nonrespondents who received the initial mailout by post. Delivery of questionnaires by hand may be an effective way to increase response rates in epidemiological research, but little is to be gained by reducing questionnaire length.