- •The vast majority of meta-analyses published in the fields of medicine and epidemiology use the I-squared statistic to quantify the amount of heterogeneity.
- •While this interpretation of I-squared is ubiquitous, it is nevertheless a fundamental mistake. I-squared does not tell us how much the effect size varies.
- •The statistic that does tell us how much the effect size varies is the prediction interval.
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Declaration of interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.