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01.12.2006 | Research | Ausgabe 1/2006 Open Access

Trials 1/2006

What influences recruitment to randomised controlled trials? A review of trials funded by two UK funding agencies

Trials > Ausgabe 1/2006
Alison M McDonald, Rosemary C Knight, Marion K Campbell, Vikki A Entwistle, Adrian M Grant, Jonathan A Cook, Diana R Elbourne, David Francis, Jo Garcia, Ian Roberts, Claire Snowdon
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Electronic supplementary material

The online version of this article (doi:10.​1186/​1745-6215-7-9) contains supplementary material, which is available to authorized users.

Competing interests

MC, DE, IR, JG, AG and AM all hold research grants for multicentre trials from the MRC and, or, the HTA Programme. AM and RK have received salary support from MRC trial grants in the past.

Authors' contributions

All STEPS Group members contributed to the project – the idea for the study was jointly conceived by the Principal Investigator, Marion Campbell (MKC) (guarantor), with Adrian Grant (AMG), Vikki Entwistle (VAE), Diana Elbourne (DE), Jo Garcia (JG), Claire Snowdon (CS), Ian Roberts (IR) and David Francis (DF). Alison McDonald (AMM) and Rosemary Knight (RCK), together with the other STEPS members, helped to design the study and did the data extraction. Jonathan Cook (JAC) undertook the analysis and, together with all group members, interpretation of data. All authors contributed to the final manuscript.



A commonly reported problem with the conduct of multicentre randomised controlled trials (RCTs) is that recruitment is often slower or more difficult than expected, with many trials failing to reach their planned sample size within the timescale and funding originally envisaged. The aim of this study was to explore factors that may have been associated with good and poor recruitment in a cohort of multicentre trials funded by two public bodies: the UK Medical Research Council (MRC) and the Health Technology Assessment (HTA) Programme.


The cohort of trials was identified from the administrative databases held by the two funding bodies. 114 trials that recruited participants between 1994 and 2002 met the inclusion criteria. The full scientific applications and subsequent trial reports submitted by the trial teams to the funders provided the principal data sources. Associations between trial characteristics and recruitment success were tested using the Chi-squared test, or Fisher's exact test where appropriate.


Less than a third (31%) of the trials achieved their original recruitment target and half (53%) were awarded an extension. The proportion achieving targets did not appear to improve over time. The overall start to recruitment was delayed in 47 (41%) trials and early recruitment problems were identified in 77 (63%) trials. The inter-relationship between trial features and recruitment success was complex. A variety of strategies were employed to try to increase recruitment, but their success could not be assessed.


Recruitment problems are complex and challenging. Many of the trials in the cohort experienced recruitment difficulties. Trials often required extended recruitment periods (sometimes supported by additional funds). While this is of continuing concern, success in addressing the trial question may be more important than recruitment alone.
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