Background: Postal questionnaires are simple and economical for collecting outcome data for randomised controlled trials (RCTs) but are prone to non-response. In the RECORD trial (a large pragmatic publicly funded RCT in UK) non-responders were sent a reminder and another questionnaire at 1 year, of which 40% were returned. In subsequent years we investigated the effect of an advance telephone call to non-responders on responses rate to reminder questionnaires and the next questionnaire 4 months later.
Methods: Non-responders to annual questionnaires were randomised to receive a telephone call from the trial office ahead of the reminder questionnaire in addition to the usual reminder schedule (n=390) or to a control group that received the usual reminder schedule only (n=363). The primary outcome was response to the reminder questionnaire within 21 days; secondary outcomes were response to a questionnaire 4 months later; completeness of quality of life instruments; and the number of participants declining further follow-up. Results are presented as odds ratios from a logistic regression intention-to-treat (ITT) analysis and then percentage difference and 95% confidence intervals (CI) for both ITT and average treatment effect on the treated (ATT) analyses.
Results: The proportions that responded were 67.8% (265/390) in the intervention group compared to 62.5% (227/363) in the control group. The ITT estimate was a 5.4% increase (95% CI -1.4 to 12.2). Four months later percentages responding were 51.8% (202) and 42.7% (155). The ITT estimate was a 9.1% increase (95% CI 2.0 to 16.2). In the intervention group 12.3% (48/390) of participants were not telephoned because questionnaires were returned before the scheduled telephone call. ATT estimates adjusting for this were 6.2% (95% CI -1.6 to 14.0) and 10.4% (95% CI 2.2 to 18.5), respectively.
Conclusions: The telephone call resulted in a slight increase in response to the reminder questionnaire, however at 4 months later the proportion in the telephoned group responding was greater. This study suggests that pre-notification telephone calls may only be worthwhile if further questionnaires are to be sent out soon after reminder questionnaires.
Trial registration: Current Clinical Trials ISRCTN51647438.