title: Selective reporting bias of harm outcomes within studies: findings from a cohort of systematic reviews.
abstract: OBJECTIVE
  To determine the extent and nature of selective non-reporting of harm outcomes in clinical studies that were eligible for inclusion in a cohort of systematic reviews.
  
  
  METHODS
  Cohort study of systematic reviews from two databases.
  
  
  METHODS
  Outcome reporting bias in trials for harm outcomes (ORBIT II) in systematic reviews from the Cochrane Library and a separate cohort of systematic reviews of adverse events.
  
  
  METHODS
  92 systematic reviews of randomised controlled trials and non-randomised studies published in the Cochrane Library between issue 9, 2012 and issue 2, 2013 (Cochrane cohort) and 230 systematic reviews published between 1 January 2007 and 31 December 2011 in other publications, synthesising data on harm outcomes (adverse event cohort).
  
  
  METHODS
  A 13 point classification system for missing outcome data on harm was developed and applied to the studies.
  
  
  RESULTS
  86% (79/92) of reviews in the Cochrane cohort did not include full data from the main harm outcome of interest of each review for all of the eligible studies included within that review; 76% (173/230) for the adverse event cohort. Overall, the single primary harm outcome was inadequately reported in 76% (705/931) of the studies included in the 92 reviews from the Cochrane cohort and not reported in 47% (4159/8837) of the 230 reviews in the adverse event cohort. In a sample of primary studies not reporting on the single primary harm outcome in the review, scrutiny of the study publication revealed that outcome reporting bias was suspected in nearly two thirds (63%, 248/393).
  
  
  CONCLUSIONS
  The number of reviews suspected of outcome reporting bias as a result of missing or partially reported harm related outcomes from at least one eligible study is high. The declaration of important harms and the quality of the reporting of harm outcomes must be improved in both primary studies and systematic reviews.
authors.affiliation: Department of Public Health and Policy, University of Liverpool, Liverpool, UK.
authors.forename: Pooja
authors.initials: P
authors.lastname: Saini
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich, UK.
authors.forename: Yoon K
authors.initials: YK
authors.lastname: Loke
authors.affiliation: Department of Biostatistics, University of Liverpool, Liverpool, L69 3GA, UK.
authors.forename: Carrol
authors.initials: C
authors.lastname: Gamble
authors.affiliation: Centre for Statistics in Medicine, University of Oxford, Oxford, UK.
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Altman
authors.affiliation: Department of Biostatistics, University of Liverpool, Liverpool, L69 3GA, UK.
authors.forename: Paula R
authors.initials: PR
authors.lastname: Williamson
authors.affiliation: Department of Biostatistics, University of Liverpool, Liverpool, L69 3GA, UK jjk@liv.ac.uk.
authors.forename: Jamie J
authors.initials: JJ
authors.lastname: Kirkham
mesh_terms: D015331:Cohort Studies; D003625:Data Collection; D064420:Drug-Related Side Effects and Adverse Reactions; D006801:Humans; D010043:Outcome and Process Assessment, Health Care; D011643:Publishing; D016032:Randomized Controlled Trials as Topic; D012107:Research Design; D012196:Review Literature as Topic; D015983:Selection Bias; D016896:Treatment Outcome