Three controlled trials of interventions to increase recruitment to a randomized controlled trial of mobile phone based smoking cessation support.

BACKGROUND: Recruitment is a major challenge for trials but there is little evidence regarding interventions to increase trial recruitment. We report three controlled trials of interventions to increase recruitment to the Txt2stop trial. PURPOSE: To evaluate: Trial 1. The impact on registrations of a text message regarding an online registration facility; Trial 2. The impact on randomizations of sending pound5 with a covering letter to those eligible to join the trial; Trial 3. The impact on randomizations of text messages containing quotes from existing participants. METHODS: Single blind controlled trials with allocation concealment. INTERVENTIONS: Trial 1: A text message regarding our new online registration facility; Trial 2: A letter with pound5 enclosed; Trial 3: A series of four text messages containing quotes from participants. The control group in each trial received standard Txt2stop procedures. RESULTS: Trial 1: 3.6% (17/470) of the intervention group and 1.1% (5/467) of the control group registered for the trial, risk difference 2.5% (95% CI 0.6-4.5). 0% (0/ 470) of the intervention group and 0.2% (1/467) of the control group registered successfully online, risk difference -0.2 (95% CI -0.6-0.2); Trial 2: 4.5% (11/246) of the intervention group and 0.4% (1/245) of the control group were randomized into the Txt2stop trial, risk difference 4.0% (95% CI 1.4-6.7); Trial 3: 3.5% (14/405) of the intervention group and 0% (0/406) of the control group were randomized into the Txt2stop trial, risk difference 3.5 (95% CI 1.7-5.2). LIMITATIONS: There were no baseline data available for trial 1. Allocation of participant IDs in trials 2 and 3 were systematic. CONCLUSION: Sending a text message about an online registration facility increased registrations to Txt2stop, but did not increase online registrations. Sending a pound5 reimbursement for participants' time and sending text messages containing quotes from existing participants increased randomizations into the Txt2stop trial. Clinical Trials 2010; 7: 265-273. http://ctj.sagepub.com.