Reports of difficulties recruiting to RCTs
| Authors | Year | Findings |
| Charleson and Horwitz4 | 1984 | A study of 41 trials listed with the National Institutes of Health (USA) showed that a third of trials recruited <75% of their planned sample. |
| Easterbrook and Matthews5 | 1992 | A review of 720 research projects approved by the Central Oxford Research Ethics Committee 1984–1987 (UK). Report states that the main reason for abandoning a study was due to difficulties recruiting study participants. |
| Wilson et al6 | 2000 | A study of recruitment of primary care practices to an endoscopy trial. Of 90 practices contacted, 43 agreed to take part, 31 recruited at least one patient and only 23 recruited more than five patients. |
| Foy et al7 | 2003 | A study of seven primary care trials of dyspepsia management in the UK. Only one study reached its recruitment target; five recruited <50% of target and three of these closed prematurely. |
| McDonald et al8 | 2006 | A study of 114 RCTs funded by two UK funding bodies 1994–2002. Thirty-one per cent of trials achieved their original recruitment target. Fifty-three per cent were extended due to recruitment problems. Early recruitment problems were identified in 63% of the trials. |
| Bower et al9 | 2007 | A survey of published primary care trials in the UK. Less than one third of trials recruited to their original timescale. |
| Raftery et al10 | 2008 | Data held by the National Coordinating Centre for Health Technology Assessment (UK) show that two thirds of funded trials fail to pass 80% of their recruitment target. |
| Toerien et al11 | 2009 | Review of all reports of RCTs published in July–December 2004 in six major journals. Of 133 trials, 21% that reported sample size calculations failed to achieve adequate numbers at randomisation and 48% at outcome assessment. |
RCT, randomised controlled trials.