title: The use of unequal randomisation in clinical trials--An update.
abstract: OBJECTIVE
  To update a 2005 review of the reasons researchers have given for the use of unequal randomisation in randomised controlled trials (RCTs).
  
  
  METHODS
  Intervention being tested; type of study; number of participants; randomisation ratio; sample size calculation and reason given for using unequal randomisation.
  
  
  METHODS
  Review of trials using unequal randomisation.
  Cochrane library, Medline and CINAHL.
  
  
  RESULTS
  A total of 86 trials were identified. Of these 82 trials (95%) recruited patients in favour of the experimental group. Various reasons for the use of unequal randomisation were given including: gaining treatment experience; identification of adverse events; ethical; logistic and enhancing recruitment. No trial reported explicitly used it for cost-effectiveness. Most of the papers (i.e. 47, 55%) did not state why they had used unequal randomisation and only 38 trials (44%) appeared to have taken the unequal randomisation into account in their sample size calculation.
  
  
  CONCLUSIONS
  Most studies did not mention the rationale for unequal allocation, and a significant proportion did not appear to account for it in the sample size calculations. Unlike the previous review economic considerations were not stated as a rationale for its use. A number of trials used it to enhance recruitment, although this has not been tested.
authors.affiliation: Department of Health Sciences, University of York, York YO10 5DD, United Kingdom. Electronic address: emily.peckham@york.ac.uk.
authors.forename: Emily
authors.initials: E
authors.lastname: Peckham
authors.affiliation: Department of Health Sciences, University of York, York YO10 5DD, United Kingdom.
authors.forename: Sally
authors.initials: S
authors.lastname: Brabyn
authors.affiliation: Department of Health Sciences, University of York, York YO10 5DD, United Kingdom.
authors.forename: Liz
authors.initials: L
authors.lastname: Cook
authors.affiliation: Department of Health Sciences, University of York, York YO10 5DD, United Kingdom.
authors.forename: Thomas
authors.initials: T
authors.lastname: Devlin
authors.affiliation: School of Nursing, Midwifery and Social Work, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom.
authors.forename: Jo
authors.initials: J
authors.lastname: Dumville
authors.affiliation: Department of Health Sciences, University of York, York YO10 5DD, United Kingdom.
authors.forename: David J
authors.initials: DJ
authors.lastname: Torgerson
mesh_terms: D006801:Humans; D059032:Learning Curve; D018579:Patient Selection; D016032:Randomized Controlled Trials as Topic / Q000191:economics / Q000941:ethics / Q000379:methods*; D012107:Research Design; D018401:Sample Size
keywords: Randomised controlled trials; Unequal randomisation