title: A third of systematic reviews changed or did not specify the primary outcome: a PROSPERO register study.
abstract: To examine outcome reporting bias of systematic reviews registered in PROSPERO.
  
  
  
  Retrospective cohort study. The primary outcomes from systematic review publications were compared with those reported in the corresponding PROSPERO records; discrepancies in the primary outcomes were assessed as upgrades, additions, omissions, or downgrades. Relative risks (RRs) and 95% confidence intervals (CI) were calculated to determine the likelihood of having a change in primary outcome when the meta-analysis result was favorable and statistically significant.
  
  
  
  Ninety-six systematic reviews were published. A discrepancy in the primary outcome occurred in 32% of the included reviews and 39% of the reviews did not explicitly specify a primary outcome(s); 6% of the primary outcomes were omitted. There was no significant increased risk of adding/upgrading (RR, 2.14; 95% CI: 0.53, 8.63) or decreased risk of downgrading (RR, 0.76; 95% CI: 0.27, 2.17) an outcome when the meta-analysis result was favorable and statistically significant. As well, there was no significant increased risk of adding/upgrading (RR, 0.89; 95% CI: 0.31, 2.53) or decreased risk of downgrading (RR, 0.56; 95% CI: 0.29, 1.08) an outcome when the conclusion was positive.
  
  
  
  We recommend review authors carefully consider primary outcome selection, and journals are encouraged to focus acceptance on registered systematic reviews.
authors.affiliation: Knowledge Translation Program, Li Ka Shing Knowledge Institute, St. Michael's Hospital, 209 Victoria Street, East Building, Toronto, Ontario M5B 1T8, Canada; Epidemiology Division, Dalla Lana School of Public Health, University of Toronto, 155 College Street, 6th Floor, Toronto, Ontario M5T 3M7, Canada. Electronic address: triccoa@smh.ca.
authors.forename: Andrea C
authors.initials: AC
authors.lastname: Tricco
authors.affiliation: Knowledge Translation Program, Li Ka Shing Knowledge Institute, St. Michael's Hospital, 209 Victoria Street, East Building, Toronto, Ontario M5B 1T8, Canada.
authors.forename: Elise
authors.initials: E
authors.lastname: Cogo
authors.affiliation: School of Public Health & Preventive Medicine, The Alfred Centre, Monash University, Level 6, 99 Commercial Road, Melbourne, Victoria 3004, Australia.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Page
authors.affiliation: Canadian Agency for Drugs and Technologies in Health (CADTH), 865 Carling Avenue Suite 600, Ottawa, Ontario K1S 5S8, Canada; Department of Epidemiology and Community Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada.
authors.forename: Julie
authors.initials: J
authors.lastname: Polisena
authors.affiliation: Centre for Reviews and Dissemination, University of York, Heslington, York YO10 5DD, United Kingdom.
authors.forename: Alison
authors.initials: A
authors.lastname: Booth
authors.affiliation: Department of Biostatistics, Institute of Translational Medicine, University of Liverpool, Crown Street, Liverpool L69 3BX, United Kingdom.
authors.forename: Kerry
authors.initials: K
authors.lastname: Dwan
authors.affiliation: Knowledge Translation Program, Li Ka Shing Knowledge Institute, St. Michael's Hospital, 209 Victoria Street, East Building, Toronto, Ontario M5B 1T8, Canada.
authors.forename: Heather
authors.initials: H
authors.lastname: MacDonald
authors.affiliation: Canadian Agency for Drugs and Technologies in Health (CADTH), 865 Carling Avenue Suite 600, Ottawa, Ontario K1S 5S8, Canada.
authors.forename: Tammy J
authors.initials: TJ
authors.lastname: Clifford
authors.affiliation: Centre for Reviews and Dissemination, University of York, Heslington, York YO10 5DD, United Kingdom.
authors.forename: Lesley A
authors.initials: LA
authors.lastname: Stewart
authors.affiliation: Knowledge Translation Program, Li Ka Shing Knowledge Institute, St. Michael's Hospital, 209 Victoria Street, East Building, Toronto, Ontario M5B 1T8, Canada; Department of Geriatric Medicine, University of Toronto, 27 King's College Circle, Toronto, Ontario M5S 1A1, Canada.
authors.forename: Sharon E
authors.initials: SE
authors.lastname: Straus
authors.affiliation: Ottawa Methods Centre, Ottawa Hospital Research Institute, The Ottawa Hospital, 501 Smyth Road, PO Box 201B, Ottawa, Ontario K1H 8L6, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Moher
mesh_terms: D015982:Bias; D015331:Cohort Studies; D015340:Epidemiologic Research Design; D006801:Humans; D017063:Outcome Assessment, Health Care / Q000379:methods* / Q000706:statistics & numerical data*; D012042:Registries / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D012196:Review Literature as Topic; D012306:Risk
keywords: Bias; Methodology; Outcome reporting bias; Quality; Reporting; Systematic reviews