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Hello, I have a non-statistician colleague who asked for some advice on an approach and I thought I would consult the boards for a second opinion. S/he wants to do a meta-analysis using five papers on the same rare event (key point) but three use RR while the other two use OR. Can anyone think of an immediate reason why it would be a bad idea to use RRs and ORs interchangeably in such a meta-analysis?

Thanks,

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John Dawson
Postdoctoral Scholar
University of Alabama at Birmingham
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This paper should help: "Converting an odds ratio to a range of plausible relative risks for better communication of research findings."
Go here for this BMJ 2014 paper  -->  http://www.bmj.com/content/348/bmj.f7450

From the paper:
"The odds ratio is a common measure in medical research of the effect size comparing two groups (treatments or risk factors) in terms of an outcome that is either present or absent. However, the odds ratio is poorly understood.1 23 The relative risk (also called the risk ratio) is more intuitive, but cannot be obtained from case-control studies or (except in rare instances) logistic regressions. Because the misunderstanding arises from the odds itself, simply describing it as a proportional change (for example, explaining an odds ratio of 0.8 as "treatment X was associated with a 20% reduction in the odds of the outcome") is not helpful for most people. This is a problem when communicating results to healthcare professionals and policy makers, discussing treatment options with patients, or seeking to conduct a meta-analysis of studies reporting effect sizes in a mixture of odds ratios and relative risks."

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Wayne Fischer
Statistician
University of Texas Medical Branch
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