title: What influences recruitment to randomised controlled trials? A review of trials funded by two UK funding agencies.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Health Services Research Unit, University of Aberdeen, Polwarth Building, Foresterhill, Aberdeen, UK. a.mcdonald@abdn.ac.uk
authors.forename: Alison M
authors.initials: AM
authors.lastname: McDonald
authors.forename: Rosemary C
authors.initials: RC
authors.lastname: Knight
authors.forename: Marion K
authors.initials: MK
authors.lastname: Campbell
authors.forename: Vikki A
authors.initials: VA
authors.lastname: Entwistle
authors.forename: Adrian M
authors.initials: AM
authors.lastname: Grant
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Cook
authors.forename: Diana R
authors.initials: DR
authors.lastname: Elbourne
authors.forename: David
authors.initials: D
authors.lastname: Francis
authors.forename: Jo
authors.initials: J
authors.lastname: Garcia
authors.forename: Ian
authors.initials: I
authors.lastname: Roberts
authors.forename: Claire
authors.initials: C
authors.lastname: Snowdon