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J Clin Epidemiol. 2009 Feb;62(2):115-22. doi: 10.1016/j.jclinepi.2008.05.014.

Synthesis of observational studies should consider credibility ceilings.

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  • 1The Clinical Trials and Evidence-Based Medicine Unit, Department of Hygiene and Epidemiology, University of Ioannina, School of Medicine, Ioannina, Greece.

Abstract

OBJECTIVE:

Meta-analyses of observational studies often get spuriously precise results. We aimed to factor this skepticism in meta-analysis calculations.

STUDY DESIGN AND SETTING:

We developed a simple sensitivity analysis starting from the assumption that any single observational study cannot give us more than a maximum certainty c% (called credibility ceiling) that an effect is in a particular direction and not in the other. Each study included in meta-analysis is adjusted for different credibility ceilings c and the consistency of the conclusion examined. We applied the method in three meta-analyses of observational studies with nominally statistically significant summary effects (mortality with teaching versus nonteaching health care; risk of non-Hodgkin's lymphoma with hair dyes; mortality with omega-3 fatty acids).

RESULTS:

Between-study heterogeneity I(2) estimates dropped from 36%-72% without a ceiling effect to 0% with ceilings of 9%, 4%, and 4% in the three meta-analyses, respectively. Nominal statistical significance was lost with ceilings of 10%, 8%, and 11%, respectively. The likelihood ratios suggested that even with minimal ceiling effects, there was no strong support for the credibility of each of these three associations.

CONCLUSIONS:

Consideration of credibility ceilings allows conservative interpretation of observational evidence and can be applied routinely to meta-analyses of observational studies.

PMID:
19131013
[PubMed - indexed for MEDLINE]
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