title: A rapid review indicated higher recruitment rates in treatment trials than in prevention trials.
abstract: OBJECTIVE
  To test the hypothesis that the percentage of patients screened that randomize differs between prevention and therapy trials.
  
  
  METHODS
  Rapid review of randomized controlled trials (RCTs) identified through published systematic reviews in August 2013. Individually randomized, parallel group controlled RCTs were eligible if they evaluated metformin monotherapy or exercise for the prevention or treatment of type 2 diabetes. Numbers of patients screened and randomized were extracted by a single reviewer. Percentages were calculated for each study for those randomized: as a function of those approached, screened, and eligible. Percentages (95% confidence intervals) from each individual study were weighted according to the denominator and pooled rates calculated. Statistical heterogeneity was assessed using I(2).
  
  
  RESULTS
  The percentage of those screened who subsequently randomized was 6.2% (6.0%, 6.4%; 3 studies, I(2) = 100.0%) for metformin prevention trials; 50.7% (49.9%, 51.4%; 21 studies, I(2) = 99.6%) for metformin treatment trials; 4.8% (4.7%, 4.8%; 14 studies, I(2) = 99.9%) for exercise prevention trials; and 43.3% (42.6%, 43.9%; 28 studies, I(2) = 99.8%) for exercise treatment trials.
  
  
  CONCLUSIONS
  This study provides qualified support for the hypothesis that prevention trials recruit a smaller proportion of those screened than treatment trials. Statistical heterogeneity associated with pooled estimates and other study limitations is discussed.
authors.affiliation: The School of Health and Related Research (ScHARR), Clinical Trials Research Unit, University of Sheffield, Regent Court, 30 Regent Street, Sheffield, S1 4DA, UK.
authors.forename: Cindy L
authors.initials: CL
authors.lastname: Cooper
authors.affiliation: The School of Health and Related Research (ScHARR), Clinical Trials Research Unit, University of Sheffield, Regent Court, 30 Regent Street, Sheffield, S1 4DA, UK. Electronic address: d.hind@sheffield.ac.uk.
authors.forename: Daniel
authors.initials: D
authors.lastname: Hind
authors.affiliation: The School of Health and Related Research (ScHARR), University of Sheffield, Regent Court, 30 Regent Street, Sheffield, S1 4DA, UK.
authors.forename: Rosie
authors.initials: R
authors.lastname: Duncan
authors.affiliation: The School of Health and Related Research (ScHARR), University of Sheffield, Regent Court, 30 Regent Street, Sheffield, S1 4DA, UK.
authors.forename: Stephen
authors.initials: S
authors.lastname: Walters
authors.affiliation: The School of Health and Related Research (ScHARR), University of Sheffield, Regent Court, 30 Regent Street, Sheffield, S1 4DA, UK.
authors.forename: Adjoa
authors.initials: A
authors.lastname: Lartey
authors.affiliation: The School of Health and Related Research (ScHARR), Clinical Trials Research Unit, University of Sheffield, Regent Court, 30 Regent Street, Sheffield, S1 4DA, UK.
authors.forename: Ellen
authors.initials: E
authors.lastname: Lee
authors.affiliation: The School of Health and Related Research (ScHARR), Clinical Trials Research Unit, University of Sheffield, Regent Court, 30 Regent Street, Sheffield, S1 4DA, UK.
authors.forename: Mike
authors.initials: M
authors.lastname: Bradburn
mesh_terms: D003924:Diabetes Mellitus, Type 2 / Q000517:prevention & control* / Q000628:therapy*; D006801:Humans; D015201:Meta-Analysis as Topic; D010358:Patient Participation / Q000706:statistics & numerical data*; D018579:Patient Selection; D016032:Randomized Controlled Trials as Topic
keywords: Consent rates; Eligibility; Exercise; Prevention; RCTs; Recruitment rates; Screening failures; Treatment