Considering bias and conflicts of interest among the included studies

Isabelle Boutron, Matthew Page, Julian P T Higgins, Douglas G Altman, Andreas Lundh, Asbjørn Hróbjartsson, on behalf of the Cochrane Bias Methods Group

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Abstract

Key Points: Review authors should seek to minimize bias. We draw a distinction between two places in which bias should be considered. The first is in the results of the individual studies included in a systematic review. The second is in the result of the metaanalysis (or other synthesis) of findings from the included studies. Problems with the design and execution of individual studies of healthcare interventions raise questions about the internal validity of their findings; empirical evidence provides support for this concern. An assessment of the internal validity of studies included in a Cochrane Review should emphasize the risk of bias in their results, that is, the risk that they will over-estimate or under-estimate the true intervention effect. Results of meta-analyses (or other syntheses) across studies may additionally be affected by bias due to the absence of results from studies that should have been included in the synthesis. Review authors should consider source of funding and conflicts of interest of authors of the study, which may inform the exploration of directness and heterogeneity of study results, assessment of risk of bias within studies, and assessment of risk of bias in syntheses owing to missing results.
Original languageEnglish
Title of host publicationCochrane Handbook for Systematic Reviews of Interventions
EditorsJulian P. T. Higgins, James Thomas, Jacqueline Chandler, Miranda Cumpston, Tianjing Li, Matthew Page, Vivien Welch
Place of PublicationChichester UK
PublisherWiley-Blackwell
Chapter7
Pages177-204
Number of pages28
Edition2nd
ISBN (Electronic)9781119536659
ISBN (Print)9781119536628, 9781119536611
Publication statusPublished - Sep 2019

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