title: Literature searching for randomized controlled trials used in Cochrane reviews: rapid versus exhaustive searches.
abstract: OBJECTIVE
  To analyze sources searched in Cochrane reviews, to determine the proportion of trials included in reviews that are indexed in major databases, and to compare the quality of these trials with those from other sources.
  
  
  METHODS
  All new systematic reviews in the Cochrane Library, Issue1 2001, that were restricted to randomized controlled trials (RCTs) or quasi-RCTs were selected. The sources searched in the reviews were recorded, and the trials included were checked to see whether they were indexed in four major databases. Trials not indexed were checked to determine how they could be identified. The quality of trials found in major databases was compared with those found from other sources.
  
  
  RESULTS
  The range in the number of databases searched per review ranged between one and twenty-seven. The proportion of the trials in the four databases were Cochrane Controlled Trials Register = 78.5%, MEDLINE = 68.8%, Embase = 65.0%, and Science/Social Sciences Citation Index = 60.7%. Searching another twenty-six databases after Cochrane Controlled Trials Register (CCTR), MEDLINE, and Embase only found 2.4% additional trials. There was no significant difference between trials found in the CCTR, MEDLINE, and Embase compared with other trials, with respect to adequate allocation concealment or sample size.
  
  
  CONCLUSIONS
  There was a large variation between reviews in the exhaustiveness of the literature searches. CCTR was the single best source of RCTs. Additional database searching retrieved only a small percentage of extra trials. Contacting authors and manufacturers to find unpublished trials appeared to be a more effective method of obtaining the additional better quality trials.
authors.affiliation: Wessex Institute for Health Research and Development.
authors.forename: Pamela
authors.initials: P
authors.lastname: Royle
authors.forename: Ruairidh
authors.initials: R
authors.lastname: Milne
mesh_terms: D015706:Bibliometrics; D016206:Databases, Bibliographic / Q000706:statistics & numerical data; D016247:Information Storage and Retrieval / Q000379:methods* / Q000706:statistics & numerical data; D015201:Meta-Analysis as Topic; D016032:Randomized Controlled Trials as Topic / Q000145:classification / Q000706:statistics & numerical data*; D012196:Review Literature as Topic; D013673:Technology Assessment, Biomedical / Q000379:methods