Professionally designed information materials and telephone reminders improved consent response rates: evidence from an RCT nested within a cohort study

OBJECTIVES To investigate whether different study-to-participant communication methods increase response, increase response from hard-to-engage individuals, and influence participants' consent decisions. STUDY DESIGN AND SETTING A randomized controlled trial within the Avon Longitudinal Study of Parents and Children. Cohort members were invited to re-enroll at age 18 and consent to linkage to their health and administrative records. Participants were randomized to receive one of eight combinations of three interventions: a prior-notification postcard or no contact, a standard or professionally designed consent pack, and a phone or postal reminder. The primary outcome was return of the consent form ("response"), with consent decision being the secondary outcome. RESULTS Of 1,950 participants, 806 (41%) responded. Response rates were 2.7% higher (95% confidence interval: -0.06, 5.5%; P = 0.06) among those receiving designed packs than among those receiving standard packs and 6.4% higher (2.3, 10.6%; P = 0.002) among those receiving phone reminders (compared with postal reminders). The prior-notification postcard did not influence response rates [difference = 0% (-2.8, 2.8%; P = 1.0)], and we found no evidence that the communication method influenced consent decision. CONCLUSION This trial provides evidence that communication material design can influence response rates and that phone reminders have superior cost/benefit returns over designed materials. Experimental evaluation of communications strategies and dissemination of findings may benefit cohort studies.