The effect of personalised versus non-personalised study invitations on recruitment within the ENGAGE feasibility trial: an embedded randomised controlled recruitment trial

BACKGROUND: Recruitment into clinical trials is challenging and there is a lack of evidence on effective recruitment strategies. Personalisation of invitation letters is a potentially pragmatic and feasible way of increasing recruitment rates at a low-cost. However, there is a lack of evidence concerning the effect of personalising of study invitation letters on recruitment rates. METHODS: We undertook a Study Within A Trial (SWAT) to investigate the effect of personalised versus non-personalised study invitation letters on recruitment rates into the host feasibility trial ENGAGE, a feasibility study of an internet-administered, guided, Low Intensity Cognitive-Behavioural Therapy based self-help intervention for parents of children previously treated for cancer. An intervention group (n = 254) received a personalised study invitation letter and the control group (n = 255) received a non-personalised study invitation letter. The primary outcome was the proportion of participants in the intervention group and the control group enrolled into the ENGAGE host feasibility trial. Secondary outcomes relating to the recruitment and screening process, and retention were examined. Differences in proportions between groups for the primary and secondary outcomes were estimated using logistic regression. RESULTS: Of the 509 potential participants, 56 (11.0%) were enrolled into the ENGAGE host feasibility trial: personalised: 30/254 (11.8%) and non-personalised: 26/255 (10.2%). No statistically significant effect on personalisation of enrolment was found (OR 1.18, 95% CI 0.68–2.06). No statistically significant differences were found for any secondary outcome. CONCLUSIONS: Personalisation of study invitations had no effect on recruitment. However, given the small study sample size in the present SWAT, and lack of similar embedded recruitment RCTs to enable a meta-analysis, additional SWATs to examine the personalisation of study invitation letters are warranted. TRIAL REGISTRATION: ISRCTN57233429; ISRCTN18404129; SWAT 112, Northern Ireland Hub for Trials Methodology Research SWAT repository (2018 OCT 1 1231) (https://www.qub.ac.uk/sites/TheNorthernIrelandNetworkforTrialsMethodologyResearch/FileStore/Filetoupload,939618,en.pdf). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12874-022-01553-5.