Recruitment to multicentre trials: the impact of external influences

A multicentre randomised controlled trial needs to recruit sufficiently large numbers of centres, clinicians and patients Delays in reaching recruitment targets are common and often necessitate extended recruitment periods with associated increased costs. The Scottish Back Trial and the MRC Laparoscopic Hernia Trial are used to illustrate how national clinical, economic and political factors can impact on the conduct of a multicentre trial. Changes in clinical practice, restructuring of the NHS and research and development funding, and changes in the procedures for obtaining local research ethics committee approval had adverse effects on recruitment. In addition, the extent to which changes in patient knowledge and attitudes to clinical trials could influence recruitment should not be ignored. In response to these obstacles both trials extended the recruitment period, identified additional recruitment centres and reduced the overall sample size. External factors which could compromise the successful completion of a d trial need to be recognised and addressed at an early stage.