title: Evaluation of the Cochrane tool for assessing risk of bias in randomized clinical trials: overview of published comments and analysis of user practice in Cochrane and non-Cochrane reviews.
abstract: BACKGROUND
  The Cochrane risk of bias tool for randomized clinical trials was introduced in 2008 and has frequently been commented on and used in systematic reviews. We wanted to evaluate the tool by reviewing published comments on its strengths and challenges and by describing and analysing how the tool is applied to both Cochrane and non-Cochrane systematic reviews.
  
  
  METHODS
  A review of published comments (searches in PubMed, The Cochrane Methodology Register and Google Scholar) and an observational study (100 Cochrane and 100 non-Cochrane reviews from 2014).
  
  
  RESULTS
  Our review included 68 comments, 15 of which were categorised as major. The main strengths of the tool were considered to be its aim (to assess trial conduct and not reporting), its developmental basis (wide consultation, empirical and theoretical evidence) and its transparent procedures. The challenges of the tool were mainly considered to be its choice of core bias domains (e.g. not involving funding/conflicts of interest) and issues to do with implementation (i.e. modest inter-rater agreement) and terminology. Our observational study found that the tool was used in all Cochrane reviews (100/100) and was the preferred tool in non-Cochrane reviews (31/100). Both types of reviews frequently implemented the tool in non-recommended ways. Most Cochrane reviews planned to use risk of bias assessments as basis for sensitivity analyses (70 %), but only a minority conducted such analyses (19 %) because, in many cases, few trials were assessed as having "low" risk of bias for all standard domains (6 %). The judgement of at least one risk of bias domain as "unclear" was found in 89 % of included randomized clinical trials (1103/1242).
  
  
  CONCLUSIONS
  The Cochrane tool has become the standard approach to assess risk of bias in randomized clinical trials but is frequently implemented in a non-recommended way. Based on published comments and how it is applied in practice in systematic reviews, the tool may be further improved by a revised structure and more focused guidance.
authors.affiliation: The Nordic Cochrane Centre, Rigshospitalet 7811, Blegdamsvej 9, 2100, Copenhagen, Denmark. lj@cochrane.dk.
authors.forename: Lars
authors.initials: L
authors.lastname: Jørgensen
authors.affiliation: The Nordic Cochrane Centre, Rigshospitalet 7811, Blegdamsvej 9, 2100, Copenhagen, Denmark.
authors.forename: Asger S
authors.initials: AS
authors.lastname: Paludan-Müller
authors.affiliation: The Nordic Cochrane Centre, Rigshospitalet 7811, Blegdamsvej 9, 2100, Copenhagen, Denmark.
authors.forename: David R T
authors.initials: DR
authors.lastname: Laursen
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK.|The National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care West (NIHR CLAHRC West) at University Hospitals Bristol NHS Foundation Trust, Bristol, UK.
authors.forename: Jelena
authors.initials: J
authors.lastname: Savović
authors.affiliation: Methods of Therapeutic Evaluation of Chronic Diseases Team, Epidemiology and Biostatistics, Sorbonne Paris Cité Research Centre, L'Institut National de la Santé et de la Recherche Médicale, Unite Mixte de Recherche 1153, Paris, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Boutron
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK.|The National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care West (NIHR CLAHRC West) at University Hospitals Bristol NHS Foundation Trust, Bristol, UK.
authors.forename: Jonathan A C
authors.initials: JA
authors.lastname: Sterne
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol, BS8 2PS, UK.|The National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care West (NIHR CLAHRC West) at University Hospitals Bristol NHS Foundation Trust, Bristol, UK.
authors.forename: Julian P T
authors.initials: JP
authors.lastname: Higgins
authors.affiliation: The Nordic Cochrane Centre, Rigshospitalet 7811, Blegdamsvej 9, 2100, Copenhagen, Denmark.|Research Unit for Evidence-Based Medicine, University of Southern Denmark, Odense, Denmark.
authors.forename: Asbjørn
authors.initials: A
authors.lastname: Hróbjartsson
mesh_terms: D006801:Humans; D015982:Bias; D016032:Randomized Controlled Trials as Topic; D018570:Risk Assessment; D000078202:Systematic Reviews as Topic
keywords: Bias; Cochrane; Comment; Randomized clinical trial; Systematic review; Tool; User practice