Telephone reminders are effective in recruiting nonresponding patients to randomized controlled trials

Studies investigating means of recruiting participants to randomized controlled trials (RCTs) are sparse. We investigated the effects of telephone reminders as a recruitment strategy.

Sick-listed employees received a written invitation to participate in a study comparing standard treatments with a solution-focused follow-up and were randomly allocated to an intervention or control group (n=703). Those who did not respond within 2 weeks received either 'no reminder' (n=242) or 'attempted telephone reminder' (n=256). Outcome was enrollment to the RCT.

An intention to recruit analysis revealed no significant differences between the groups (P=.229). An intention to phone analysis among nonresponders revealed significant differences between 'no reminder' (recruited 4.5%) and 'attempted telephone reminder' (recruited 12.1%) (P=.003, odds ratio 2.89, 95% confidence interval [CI] 1.42-5.90). An analysis of numbers needed to phone showed that to recruit one more person in this group of nonresponders, we needed to phone 13 persons (95% CI=8-33).

Systematic use of telephone calls can increase the recruitment rate among nonresponders in RCTs.