GRADE guidelines: 5. Rating the quality of evidence--publication bias.
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.
Guyatt, GH; Oxman, AD; Montori, V; Vist, G; Kunz, R; Brozek, J; Alonso-Coello, P; Djulbegovic, B; Atkins, D; Falck-Ytter, Y; Williams, JW; Meerpohl, J; Norris, SL; Akl, EA; Schünemann, HJ
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