title: Reporting characteristics of non-primary publications of results of randomized trials: a cross-sectional review.
abstract: BACKGROUND
  For a randomized trial, the primary publication is usually the one which reports the results of the primary outcome and provides consolidated data from all study centers. Other aspects of a randomized trial's findings (that is, non-primary results) are often reported in subsequent publications.
  
  
  METHODS
  We carried out a cross-sectional review of the characteristics and type of information reported in non-primary reports (n = 69) of randomized trials (indexed in PubMed core clinical journals in 2009) and whether they report pre-specified or exploratory analyses. We also compared consistency of information in non-primary publications with that reported in the primary publication.
  
  
  RESULTS
  The majority (n = 56; 81%) of non-primary publications were large, multicenter trials, published in specialty journals. Most reported subgroup analyses (n = 27; 39%), analyzing a specific subgroup of patients from the randomized trial, or reported on secondary outcomes (n = 29; 42%); 19% (n = 13) reported extended follow-up. Less than half reported details of trial registration (n = 30; 43%) or the trial protocol (n = 27; 39%) and in 41% (n = 28) it was unclear from reading the abstract that the report was not the primary publication for the trial. Non-primary publications often analyzed and reported multiple different outcomes (16% reported >20 outcomes) and in 10% (n = 7) it was unclear how many outcomes had actually been assessed; in 42% (n = 29) it was unclear whether the analyses reported were pre-specified or exploratory. Only 39% (n = 27) of non-primary publications described the primary outcome of the randomized trial, 6% (n = 4) reported its numerical results and 9% (n = 6) details of how participants were randomized.
  
  
  CONCLUSIONS
  Non-primary publications often lack important information about the randomized trial and the type of analyses conducted and whether these were pre-specified or exploratory to enable readers to accurately identify and assess the validity and reliably of the study findings. We provide recommendations for what information authors should include in non-primary reports of randomized trials.
authors.affiliation: Centre for Statistics in Medicine, University of Oxford, Botnar Recpsearch Building, Windmill Road, Oxford, UK. sally.hopewell@csm.ox.ac.uk
authors.forename: Sally
authors.initials: S
authors.lastname: Hopewell
authors.forename: Gary S
authors.initials: GS
authors.lastname: Collins
authors.forename: Allison
authors.initials: A
authors.lastname: Hirst
authors.forename: Shona
authors.initials: S
authors.lastname: Kirtley
authors.forename: Abdelouahid
authors.initials: A
authors.lastname: Tajar
authors.forename: Stephen
authors.initials: S
authors.lastname: Gerry
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Altman
mesh_terms: D022126:Access to Information; D015706:Bibliometrics; D003430:Cross-Sectional Studies; D006801:Humans; D033181:Information Dissemination; D015337:Multicenter Studies as Topic / Q000379:methods; D010506:Periodicals as Topic; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D015203:Reproducibility of Results; D012107:Research Design
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