Telephone reminders are a cost effective way to improve responses in postal health surveys

Study objective: To assess the effectiveness of a telephone reminder in increasing responses to postal surveys and to calculate the differential costs per completed questionnaire. Design: Randomised controlled trial. Setting: Australian university and rehabilitation medicine practice. Participants: The trial was conducted in 1999 among the 143 non-respondents to a questionnaire about work related neck and upper body disorders. The questionnaire was sent to two Australian female samples: 200 office workers (Sample A) and 92 former rehabilitation medicine patients (Sample B). A reminder letter, another copy of the questionnaire and a final letter were sent at two week intervals. Half of the non-respondents within each sample were randomly selected to receive a telephone reminder just after the second mailout of the questionnaire. All direct costs were calculated. Main results: Responses were significantly higher among those who received the telephone reminder intervention (relative risk 2.54, 95% confidence intervals 1.43 to 4.52). Analysed by intention to phone, 47% of non-respondents in Sample A and 38% in Sample B returned a complete questionnaire after the intervention, compared with 21% and 10%, respectively, in the control groups. For the 112 women (combined samples) who returned completed questionnaires before randomisation, the average cost per respondent was AUD14. There was a higher total cost for the intervention groups (AUD851 versus AUD386 for controls), but the significantly higher number of additional completed responses (31 versus 12) resulted in a 15% lower marginal cost per completed questionnaire in those groups. Conclusion: Telephone reminders are cost effective in improving responses to postal surveys.