title: Inclusion of nonrandomized studies in Cochrane systematic reviews was found to be in need of improvement.
abstract: OBJECTIVE
  Nonrandomized studies (NRSs) are considered to provide less reliable evidence for intervention effects. However, these are included in Cochrane reviews, despite discouragement. There has been no evaluation of when and how these designs are used. Therefore, we conducted an overview of current practice.
  
  
  METHODS
  We included all Cochrane reviews that considered NRS, conducting inclusions and data extraction in duplicate.
  
  
  RESULTS
  Of the included 202 reviews, 114 (56%) did not cite a reason for including NRS. The reasons were divided into two major categories: NRS were included because randomized controlled trials (RCTs) are wanted (N = 81, 92%) but not feasible, lacking, or insufficient alone or because RCTs are not needed (N = 7, 8%). A range of designs were included with controlled before-after studies as the most common. Most interventions were nonpharmaceutical and the settings nonmedical. For risk of bias assessment, Cochrane Effective Practice and Organisation of Care Group's checklists were used by most reviewers (38%), whereas others used a variety of checklists and self-constructed tools.
  
  
  CONCLUSIONS
  Most Cochrane reviews do not justify including NRS. When they do, most are not in line with Cochrane recommendations. Risk of bias assessment varies across reviews and needs improvement.
authors.affiliation: Cochrane OSH Review Group, Finnish Institute of Occupational Health, PO Box 301, 70701 Kuopio, Finland.
authors.forename: Sharea
authors.initials: S
authors.lastname: Ijaz
authors.affiliation: Cochrane OSH Review Group, Finnish Institute of Occupational Health, PO Box 301, 70701 Kuopio, Finland. Electronic address: jos.verbeek@ttl.fi.
authors.forename: Jos H
authors.initials: JH
authors.lastname: Verbeek
authors.affiliation: Cochrane OSH Review Group, Finnish Institute of Occupational Health, PO Box 301, 70701 Kuopio, Finland.
authors.forename: Christina
authors.initials: C
authors.lastname: Mischke
authors.affiliation: Cochrane OSH Review Group, Finnish Institute of Occupational Health, PO Box 301, 70701 Kuopio, Finland.
authors.forename: Jani
authors.initials: J
authors.lastname: Ruotsalainen
mesh_terms: D015982:Bias; D006801:Humans; D016032:Randomized Controlled Trials as Topic; D012107:Research Design / Q000592:standards*; D012196:Review Literature as Topic; D018570:Risk Assessment
keywords: Comparative effectiveness research; Epidemiologic bias; Intervention studies; Meta-analysis; Review; Systematic reviews