title: Issues relating to selective reporting when including non-randomized studies in systematic reviews on the effects of healthcare interventions.
abstract: BACKGROUND
  Selective outcome and analysis reporting (SOR and SAR) occur when only a subset of outcomes measured and analyzed in a study is fully reported, and are an important source of potential bias.
  We describe what is known about the prevalence and effects of SOR and SAR in both randomized controlled trials (RCTs) and non-randomized studies (NRS), and the effects of SOR and SAR on summary effect estimates and conclusions in systematic reviews of the effectiveness of healthcare interventions.
  Review authors should always suspect SOR and SAR in reviews that include NRS, assess primary studies for the risk of bias, and make reasonable attempts to retrieve study protocols or other documentation developed before study recruitment began. There are clues that may suggest SOR or SAR in NRS, including differences between the methods and results sections of the publication, study funder, and differences between study protocol or registration information and the study report.
  
  
  CONCLUSIONS
  Existing evidence about reporting biases in primary studies comes almost exclusively from methodological reviews of RCTs. The prevalence and impact of SOR and SAR in NRS are likely even greater than in RCTs but it is difficult to identify and confirm selective reporting in NRS. Copyright © 2012 John Wiley & Sons, Ltd.
authors.affiliation: Department of Medical Informatics and Clinical Epidemiology, Oregon Health & Science University, Portland, OR, USA.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Norris
authors.affiliation: Ottawa Hospital Research Institute, Ottawa, ON, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Moher
authors.affiliation: Bristol Heart Institute, Bristol Royal Infirmary, University of Bristol, Bristol, UK.
authors.forename: Barnaby C
authors.initials: BC
authors.lastname: Reeves
authors.affiliation: Community Information and Epidemiological Technologies, Institute of Population Health, Ottawa, ON, Canada.
authors.forename: Beverley
authors.initials: B
authors.lastname: Shea
authors.affiliation: Faculty of Medicine and Health Sciences, University of East Anglia, Norwich, UK.
authors.forename: Yoon
authors.initials: Y
authors.lastname: Loke
authors.affiliation: National Institute for Health and Clinical Excellence, London, UK.
authors.forename: Sarah
authors.initials: S
authors.lastname: Garner
authors.affiliation: School of Public Health, University of Washington, Seattle, WA, USA.
authors.forename: Laurie
authors.initials: L
authors.lastname: Anderson
authors.affiliation: Centre for Global Health, Institute of Population Health, Ottawa, ON, Canada.
authors.forename: Peter
authors.initials: P
authors.lastname: Tugwell
authors.affiliation: Centre for Global Health, Institute of Population Health, Ottawa, ON, Canada.
authors.forename: George
authors.initials: G
authors.lastname: Wells
keywords: non-randomized studies; observational studies; publication bias; reporting bias; selective outcome reporting; systematic reviews