Increasing participant recruitment into large-scale screening trials: experience from the CADET II study

Objectives Multicentre randomized trials frequently encounter difficulties in meeting their recruitment targets, resulting in extension of the trial and delays in implementation of the findings. We report on recruitment strategies implemented in a randomized evaluation of computer-aided detection in women attending routine screening in the UK Breast Screening Programme.
Setting The target population for the trial was identified from an existing NHS database of women aged 50–70 invited for routine mammography in Coventry, Manchester and Nottingham, UK. Women were asked to consent to their mammograms being randomly allocated (in a ratio of 28:1:1) to one of three film-reading protocols. Trial information was mailed to women, along with the invitation to attend screening, and informed consent was obtained at the mammography appointment. Several strategies were implemented to increase recruitment rates.

Results Recruitment rate increased significantly over time in the study (P < 0.0010 in all centres) with an overall acceptance rate of 46% of those attending screening. Mailing of the trial information sheet separate from the screening invitation in Coventry and Nottingham increased the recruitment rate, even after adjustment for the trend over time and for socioeconomic status of the attendees (P < 0.001). Extension of recruitment to mobile screening units in Nottingham, and the presence of an additional member of staff also improved recruitment (P < 0.001). Simplification of the trial information sheet had little effect. Increases in recruitment rate were not attributable to socioeconomic status of the attendees.

Conclusions In multicentre trials, monitoring of local recruitment protocols is required to ensure that each centre can maximize accrual targets.