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.
|Title of host publication||Cochrane Handbook for Systematic Reviews of Interventions|
|Editors||Julian P. T. Higgins, James Thomas, Jacqueline Chandler, Miranda Cumpston, Tianjing Li, Matthew Page, Vivien Welch|
|Place of Publication||Chichester UK|
|Number of pages||28|
|ISBN (Print)||9781119536628, 9781119536611|
|Publication status||Published - Sep 2019|