title: GRADE guidelines: 5. Rating the quality of evidence--publication bias.
abstract: In the GRADE approach, randomized trials start as high-quality evidence and observational studies as low-quality evidence, but both can be rated down if a body of evidence is associated with a high risk of publication bias. Even when individual studies included in best-evidence summaries have a low risk of bias, publication bias can result in substantial overestimates of effect. Authors should suspect publication bias when available evidence comes from a number of small studies, most of which have been commercially funded. A number of approaches based on examination of the pattern of data are available to help assess publication bias. The most popular of these is the funnel plot; all, however, have substantial limitations. Publication bias is likely frequent, and caution in the face of early results, particularly with small sample size and number of events, is warranted.
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario L8N 3Z5, Canada. guyatt@mcmaster.ca
authors.forename: Gordon H
authors.initials: GH
authors.lastname: Guyatt
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Oxman
authors.forename: Victor
authors.initials: V
authors.lastname: Montori
authors.forename: Gunn
authors.initials: G
authors.lastname: Vist
authors.forename: Regina
authors.initials: R
authors.lastname: Kunz
authors.forename: Jan
authors.initials: J
authors.lastname: Brozek
authors.forename: Pablo
authors.initials: P
authors.lastname: Alonso-Coello
authors.forename: Ben
authors.initials: B
authors.lastname: Djulbegovic
authors.forename: David
authors.initials: D
authors.lastname: Atkins
authors.forename: Yngve
authors.initials: Y
authors.lastname: Falck-Ytter
authors.forename: John W
authors.initials: JW
authors.lastname: Williams
authors.forename: Joerg
authors.initials: J
authors.lastname: Meerpohl
authors.forename: Susan L
authors.initials: SL
authors.lastname: Norris
authors.forename: Elie A
authors.initials: EA
authors.lastname: Akl
authors.forename: Holger J
authors.initials: HJ
authors.lastname: Schünemann
mesh_terms: D003430:Cross-Sectional Studies; D004345:Drug Industry; D019317:Evidence-Based Medicine / Q000592:standards*; D015201:Meta-Analysis as Topic; D017410:Practice Guidelines as Topic; D017594:Publication Bias; D016032:Randomized Controlled Trials as Topic / Q000592:standards*; D012196:Review Literature as Topic; D013223:Statistics as Topic