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Morrison et al examine the effect on questionnaire response of feeding back research findings to participants.1 As authors of the systematic review2 cited in their paper we would like to point out that we had in fact identified eight such randomised trials.3–10 The broad strategy under which these trials had been classified in our review was “non-monetary incentives”. We are currently updating our systematic review and have recently extended the search of databases to the beginning of 2003 and have contacted the authors of potentially eligible trials. A further two trials11,12 have been identified and the total of 10 trials have also been classified under the new strategy called “offer of research findings”. These trials include a total of 13 642 participants. When the results of these trials are pooled in a random effects meta analysis the odds ratio for response with research findings is 0.92 (95% CI 0.75 to 1.11). Despite omitting to refer to these previous trials, Morrison et al were justified in conducting their trial: few of such trials have been health related and none has examined the effect of this intervention when participants are being resurveyed. However, even with the inclusion of their new trial in our systematic review, uncertainty about the effect of dissemination of research findings on questionnaire response remains.
The update to our systematic review now includes a total of 372 trials of methods to influence response to postal questionnaires, classified under 98 strategies. Although many conclusions remain unchanged our updated review presents the definitive account of the evidence for which strategies may be used to improve response to postal questionnaires. The updated review will appear in the Cochrane Library later this year.