A new generation of bias in EBM

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 In the EUROPA trial  12,218 patients were randomized to receive perindopril or placebo. 9.9% of the participants in the ‘placebo’ group died or had a heart attack, whereas only 8% in the experimental group died or had a heart attack: roughly a 2% absolute effect size.  You would have to treat 50 patients with the drug to get one with a positive outcome.

According to current EBM standards, the EUROPA study provided very good evidence supporting the effects of perindopril because the study was large, randomized and double-blind. On this basis the authors of the study recommended that “all patients with coronary heart disease” should use the drug.

However, there are several problems with this and other large studies with small effects that are overlooked by standard EBM critical appraisal methods.

Exaggerating effect sizes

The authors of the EUROPA study reported the misleading relative effect size of 20% which…

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