title: Risk of bias in overviews of reviews: a scoping review of methodological guidance and four-item checklist.
abstract: OBJECTIVE
  To assess the conditions under which employing an overview of systematic reviews is likely to lead to a high risk of bias.
  
  
  METHODS
  To synthesise existing guidance concerning overview practice, a scoping review was conducted. Four electronic databases were searched with a pre-specified strategy (PROSPERO 2015:CRD42015027592) ending October 2015. Included studies needed to describe or develop overview methodology. Data were narratively synthesised to delineate areas highlighted as outstanding challenges or where methodological recommendations conflict.
  
  
  RESULTS
  Twenty-four papers met the inclusion criteria. There is emerging debate regarding overlapping systematic reviews; systematic review scope; quality of included research; updating; and synthesizing and reporting results. While three functions for overviews have been proposed-identify gaps, explore heterogeneity, summarize evidence-overviews cannot perform the first; are unlikely to achieve the second and third simultaneously; and can only perform the third under specific circumstances. Namely, when identified systematic reviews meet the following four conditions: (1) include primary trials that do not substantially overlap, (2) match overview scope, (3) are of high methodological quality, and (4) are up-to-date.
  
  
  CONCLUSIONS
  Considering the intended function of proposed overviews with the corresponding methodological conditions may improve the quality of this burgeoning publication type. Copyright © 2017 John Wiley & Sons, Ltd.
authors.affiliation: Centre for Evidence-Based Intervention, University of Oxford, Oxford, UK.
authors.forename: Madeleine
authors.identifier: http://orcid.org/0000-0003-0107-4047
authors.initials: M
authors.lastname: Ballard
authors.affiliation: Centre for Evidence-Based Intervention, University of Oxford, Oxford, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Montgomery
mesh_terms: D000465:Algorithms; D057189:Checklist; D002986:Clinical Trials as Topic; D003362:Cost-Benefit Analysis; D016208:Databases, Factual; D019317:Evidence-Based Medicine / Q000592:standards*; D006801:Humans; D017594:Publication Bias; D011642:Publications; D012107:Research Design / Q000592:standards*; D012196:Review Literature as Topic
keywords: meta-review; overview of reviews; scoping review; synthesis methods; umbrella review