Empirical evidence of bias in treatment effect estimates in controlled trials with different interventions and outcomes: meta-epidemiological study

Wood, Lesley; Egger, Matthias; Gluud, Lise Lotte; Schulz, Kenneth F; Jüni, Peter; Altman, Douglas G; Gluud, Christian; Martin, Richard M; Wood, Anthony J G; Sterne, Jonathan A C (2008). Empirical evidence of bias in treatment effect estimates in controlled trials with different interventions and outcomes: meta-epidemiological study. BMJ, 336(7644), pp. 601-5. London: BMJ Publishing Group 10.1136/bmj.39465.451748.AD

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OBJECTIVE: To examine whether the association of inadequate or unclear allocation concealment and lack of blinding with biased estimates of intervention effects varies with the nature of the intervention or outcome. DESIGN: Combined analysis of data from three meta-epidemiological studies based on collections of meta-analyses. DATA SOURCES: 146 meta-analyses including 1346 trials examining a wide range of interventions and outcomes. MAIN OUTCOME MEASURES: Ratios of odds ratios quantifying the degree of bias associated with inadequate or unclear allocation concealment, and lack of blinding, for trials with different types of intervention and outcome. A ratio of odds ratios <1 implies that inadequately concealed or non-blinded trials exaggerate intervention effect estimates. RESULTS: In trials with subjective outcomes effect estimates were exaggerated when there was inadequate or unclear allocation concealment (ratio of odds ratios 0.69 (95% CI 0.59 to 0.82)) or lack of blinding (0.75 (0.61 to 0.93)). In contrast, there was little evidence of bias in trials with objective outcomes: ratios of odds ratios 0.91 (0.80 to 1.03) for inadequate or unclear allocation concealment and 1.01 (0.92 to 1.10) for lack of blinding. There was little evidence for a difference between trials of drug and non-drug interventions. Except for trials with all cause mortality as the outcome, the magnitude of bias varied between meta-analyses. CONCLUSIONS: The average bias associated with defects in the conduct of randomised trials varies with the type of outcome. Systematic reviewers should routinely assess the risk of bias in the results of trials, and should report meta-analyses restricted to trials at low risk of bias either as the primary analysis or in conjunction with less restrictive analyses.

Item Type:	Journal Article (Original Article)
Division/Institute:	04 Faculty of Medicine > Pre-clinic Human Medicine > Institute of Social and Preventive Medicine (ISPM)
UniBE Contributor:	Egger, Matthias, Jüni, Peter
ISSN:	1756-1833
ISBN:	18316340
Publisher:	BMJ Publishing Group
Language:	English
Submitter:	Factscience Import
Date Deposited:	04 Oct 2013 15:04
Last Modified:	05 Dec 2022 14:19
Publisher DOI:	10.1136/bmj.39465.451748.AD
PubMed ID:	18316340
Web of Science ID:	000254364500034
URI:	https://boris.unibe.ch/id/eprint/27775 (FactScience: 111487)