Do messages of scarcity increase trial recruitment?

INTRODUCTION: Psychological theory suggests that participants may be more likely to volunteer to join a clinical trial if they perceive places in the trial are a scarce commodity. MATERIAL AND METHODS: We conducted a single blind, randomized controlled trial to test recruitment strategies within the larger txt2stop smoking cessation trial. 1862 people who were eligible for the txt2stop trial but had not yet consented to join were randomized to receive either A) a reminder about the txt2stop trial plus a message that there were only 300 places left, or B) a reminder about the trial only. The outcome was the participant's consent to join the txt2stop trial 3days after messages were sent. RESULTS: Of 895 participants randomized to the intervention group, 90 (10.1%) had consented to join the txt2stop trial. Of the 967 participants randomized to the control group, 67 (6.9%) had consented to join the txt2stop trial (OR=1.50, 95% CI 1.07-2.12). DISCUSSION: Scarcity messages were an effective way to increase recruitment into the txt2stop trial and could be relevant to other trials. CONCLUSIONS: Communicating scarcity is an effective way to increase trial recruitment.