title: Trial registration numbers are underreported in biomedical publications.
abstract: BACKGROUND
  Since September 2005, the International Committee of Medical Journal Editors (ICMJE) has required that randomised controlled trials (RCTs) are prospectively registered in a publicly accessible database. After registration, a trial registration number (TRN) is assigned to each RCT, which should make it easier to identify future publications and cross-check published results with associated registry entries, as long as the unique identification number is reported in the article.
  
  
  OBJECTIVE
  Our primary objective was to evaluate the reporting of trial registration numbers in biomedical publications. Secondary objectives were to evaluate how many published RCTs had been registered and how many registered RCTs had resulted in a publication, using a sample of trials from the Netherlands Trials Register (NTR).
  
  
  METHODS
  TWO DIFFERENT SAMPLES OF RCTS WERE EXAMINED: 1) RCTs published in November 2010 in core clinical journals identified in MEDLINE; 2) RCTs registered in the NTR with a latest expected end date of 31 August 2008.
  
  
  RESULTS
  Fifty-five percent (166/302) of the reports of RCTs found in MEDLINE and 60% (186/312) of the published reports of RCTs from the NTR cohort contained a TRN. In both samples, reporting of a TRN was more likely in RCTs published in ICMJE member journals as compared to non-ICMJE member journals (MEDLINE 58% vs. 45%; NTR: 70% vs. 49%). Thirty-nine percent of published RCTs in the MEDLINE sample appear not to have been registered, and 48% of RCTs registered in the NTR seemed not to have been published at least two years after the expected date for study completion.
  
  
  CONCLUSIONS
  Our results show that further promotion and implementation of trial registration and accurate reporting of TRN is still needed. This might be helped by inclusion of the TRN as an item on the CONSORT checklist.
authors.affiliation: Dutch Cochrane Centre, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. f.t.vandewetering@amc.uva.nl
authors.forename: Fleur T
authors.initials: FT
authors.lastname: van de Wetering
authors.forename: Rob J P M
authors.initials: RJ
authors.lastname: Scholten
authors.forename: Tamara
authors.initials: T
authors.lastname: Haring
authors.forename: Michael
authors.initials: M
authors.lastname: Clarke
authors.forename: Lotty
authors.initials: L
authors.lastname: Hooft
mesh_terms: D035843:Biomedical Research / Q000706:statistics & numerical data*; D002986:Clinical Trials as Topic; D006801:Humans; D011643:Publishing / Q000706:statistics & numerical data*; D012042:Registries