Pre-notification of trial participants to improve response rates retention (SWAT 28); a study within a trial (SWAT) embedded in PROFHER-2

Background Randomised Controlled Trials (RCTs) are the most robust method to test new or existing interventions. Recruitment and retention are crucial aspects to their success but are often challenging. Methodological changes to RCTs are often tested by Studies Within A Trial (SWATs). To date there is mixed evidence supporting the use of prenotification newsletters to boost retention. This SWAT aimed to assess this intervention within the PROFHER-2 trial. Methods A two-arm parallel group SWAT embedded at the 24-months follow-up for PROFHER-2 – a RCT evaluating treatment methods for a 3- or 4- part proximal humerus fractures in patients over 65 years. Participants were randomised (1:1) to either receive a newsletter 2-to-4 weeks prior to their 24-months questionnaire, or not. The results have been combined in a meta-analysis with existing evidence. Results There was no evidence of a difference in retention (OR 2.17, 95% CI 0.21-22.02, p = 0.51). Similarly, there was no statistically significant difference in the completion of the primary outcome of the returned questionnaires (OR 0.72, 95% CI 0.04–12.70, p = 0.82), nor the proximity of completion (HR 1.23, 95% CI 0.74 – 2.05, p = 0.43). This result is similar to that seen in two of the four previous evaluations of this SWAT. Conclusion Sending a newsletter as a prenotification to a questionnaire in a RCT does not improve the retention rates. However, the sample size for this piece of work is small, and the retention rates were high (94%). When combined with the existing evidence, there is no evidence of an effect.