title: An introduction to methodological issues when including non-randomised studies in systematic reviews on the effects of interventions.
abstract: BACKGROUND
  Methods need to be further developed to include non-randomised studies (NRS) in systematic reviews of the effects of health care interventions. NRS are often required to answer questions about harms and interventions for which evidence from randomised controlled trials (RCTs) is not available. Methods used to review randomised controlled trials may be inappropriate or insufficient for NRS.
  
  
  OBJECTIVE
  A workshop was convened to discuss relevant methodological issues. Participants were invited from important stakeholder constituencies, including methods and review groups of the Cochrane and Campbell Collaborations, the Cochrane Editorial Unit and organisations that commission reviews and make health policy decisions. The aim was to discuss methods for reviewing evidence when including NRS and to formulate methodological guidance for review authors.
  The workshop was structured around four sessions on topics considered in advance to be most critical: (i) study designs and bias; (ii) confounding and meta-analysis; (iii) selective reporting; and (iv) applicability. These sessions were scheduled between introductory and concluding sessions.
  
  
  CONCLUSIONS
  This is the first of six papers and provides an overview. Subsequent papers describe the discussions and conclusions from the four main sessions (papers 2 to 5) and summarise the proposed guidance into lists of issues for review authors to consider (paper 6). Copyright © 2013 John Wiley & Sons, Ltd.
authors.affiliation: Clinical Trials and Evaluation Unit, School of Clinical Sciences, University of Bristol, UK.
authors.forename: Barnaby C
authors.initials: BC
authors.lastname: Reeves
authors.affiliation: MRC Biostatistics Unit, Cambridge, UK.|Centre for Reviews and Dissemination, University of York, UK.
authors.forename: Julian P T
authors.initials: JP
authors.lastname: Higgins
authors.affiliation: Health Services Research Unit, University of Aberdeen, UK.
authors.forename: Craig
authors.initials: C
authors.lastname: Ramsay
authors.affiliation: Community Information and Epidemiological Technologies, Institute of Population Health, Ottawa, Canada.
authors.forename: Beverley
authors.initials: B
authors.lastname: Shea
authors.affiliation: Centre for Global Health, Institute of Population Health, Ottawa, Canada.
authors.forename: Peter
authors.initials: P
authors.lastname: Tugwell
authors.affiliation: Department of Epidemiology and Community Medicine, University of Ottawa, Canada.
authors.forename: George A
authors.initials: GA
authors.lastname: Wells
keywords: benefit; harm; non-randomised study; systematic review