Bias due to changes in specified outcomes during the systematic review process

Ref ID 539
First Author J. J. Kirkham
Journal PLOS ONE
Year Of Publishing 2010
URL https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2842442/pdf/pone.0009810.pdf
Keywords • General medical
• Protocols
• Cochrane
• Multiplicity
Problem(s) • Failure to define clinically meaningful outcomes
• Undocumented or unjustified deviations to the review protocol
• Multiplicity of outcomes and lack of pre-specification for outcome reporting
Article Type Empirical
Article Subtype Meta-epidemiological analysis
First Author Country United Kingdom
Aim To assess discrepancies between primary outcomes listed in Cochrane review protocols and those in the subsequent completed reviews published in consecutive issues on the Cochrane Library between 2006 and 2007.
Level of Investigation Analytical
Summary of Findings 22% of the 297 included protocol/review pairings contained a discrepancy in at least one outcome measure, of which 75% were attributable to changes in the primary outcome measure. Where lead authors could recall a reason for the discrepancy in the primary outcome, 29% of these reviews made changes after knowledge of the results from individual trials. Only 6% of reviews with an outcome discrepancy described the reason for the change in the review.
Number of systematic reviews included 297
Number of eligible systematic reviews assessed 309
Treatment impacted Yes
Treatment impacted description
Interpretation impacted Yes
Interpretation impacted description Outcomes that were promoted in the review were more likely to be significant than if there was no discrepancy (relative risk 1.66 95% CI (1.10, 2.49), p = 0.02).