Including the questionnaire with an invitation letter did not improve a telephone survey's response rate

Objective: To determine whether including the study questionnaire with a letter of invitation improves the response rate in a telephone-based survey. Study Design and Setting: This randomized controlled trial was part of a larger study to assess patient preferences for novel and controversial treatments for inflammatory bowel disease at Royal Prince Alfred Hospital, a tertiary referral teaching hospital in Sydney, Australia. Results: Of 270 eligible patients, 124 (46%) were randomized to receive the questionnaire plus invitation whereas 146 (54%) were in the control group receiving a letter of invitation only. The consent rate was 26% for those receiving the questionnaire and 36% for the control group. The odds ratio for consent to participate among those sent the questionnaire to those not sent the questionnaire was 0.63 (95% CI = 0.37-1.07). Conclusion: This study found that the advance mailing of a questionnaire to potential participants in a telephone survey reduced the likelihood of their participation. (C) 2007 Elsevier Inc. All rights reserved.