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Abstract
Background: The Cochrane 'Risk of bias' tool is used for evaluating the risk of bias of randomized controlled trials included in systematic review. It contains six domains (including seven items): selection bias (random sequence generation and allocation concealment), performance bias (blinding of participants and personnel), detection bias (blinding of outcome assessment), attrition bias (incomplete outcome data), reporting bias (selective outcome reporting) and other sources of bias. The criteria of the six former items are defined explicitly in the Cochrane Handbook for Systematic Reviews of Interventions, but those for 'other bias' are not.
Objectives: To investigate the criteria of 'other bias' of the Cochrane Risk of Bias Tool for further assessment of risk of bias of randomized controlled trials in systematic reviews.
Methods: We handsearched for systematic reviews published between 1 January 2012 to 31 December 2014 in the Cochrane Database of Systematic Review, Annals of Internal Medicine, Annals of Surgery, The Journal of the American Medical Association, The Lancet, and the BMJ. The included randomized controlled trials were assessed by the Cochrane 'Risk of bias' tool. Two reviewers completed the handsearching, screening and data extraction independently.
Results: We included 340 systematic reviews, of which 250 (74%) were Cochrane Reviews and 90 (26%) non-Cochrane reviews. In total, 3342 primary studies included in 233 (69%) systematic reviews were judged to have 'other bias'. Of those, 723 (22%) were assessed as being at high risk, of which 538 (16%) were reported with the causes that were integrated into 67 causes. A total of 55 causes (from 167 original studies included in 108 systematic reviews) overlapped with the former six items such as random sequence generation, etc. In addition, the chief cause of 'other bias' was potential conflicts of interest.
Conclusions: The causes of 'other bias' are varied in current systematic reviews, but most of them overlap with the other six bias items including random sequence generation, etc.
Objectives: To investigate the criteria of 'other bias' of the Cochrane Risk of Bias Tool for further assessment of risk of bias of randomized controlled trials in systematic reviews.
Methods: We handsearched for systematic reviews published between 1 January 2012 to 31 December 2014 in the Cochrane Database of Systematic Review, Annals of Internal Medicine, Annals of Surgery, The Journal of the American Medical Association, The Lancet, and the BMJ. The included randomized controlled trials were assessed by the Cochrane 'Risk of bias' tool. Two reviewers completed the handsearching, screening and data extraction independently.
Results: We included 340 systematic reviews, of which 250 (74%) were Cochrane Reviews and 90 (26%) non-Cochrane reviews. In total, 3342 primary studies included in 233 (69%) systematic reviews were judged to have 'other bias'. Of those, 723 (22%) were assessed as being at high risk, of which 538 (16%) were reported with the causes that were integrated into 67 causes. A total of 55 causes (from 167 original studies included in 108 systematic reviews) overlapped with the former six items such as random sequence generation, etc. In addition, the chief cause of 'other bias' was potential conflicts of interest.
Conclusions: The causes of 'other bias' are varied in current systematic reviews, but most of them overlap with the other six bias items including random sequence generation, etc.