Recruitment to multicentre trials

To obtain clear and definitive answers to clinically important questions, randomised controlled trials (RCTs) with sufficiently large sample sizes are needed, which usually requires recruitment in several centres. A common problem in multicentre trials is that recruitment is slower or more difficult than expected, and many trials fail to reach their planned sample size within the timescale and funding originally envisaged. If the target sample size is not achieved, the trial has less power to discover differences between the groups, so the results may be less useful. If recruitment has to be extended to reach the required sample size, the trial will take longer and cost more than planned, delaying the use of the results in clinical practice. The more expensive trials become and the longer they take, the fewer can be conducted with the funding and resources available. It is therefore important to understand the reasons for poor recruitment and find effective strategies to improve it.