The take-home message is that meta-analyses that include multiple studies with practically identical results should be viewed with great caution. Fabrication, double publication, plagiarism, variants of salami publication,5 allegiance or confirmation bias, or other questionable practices may sometimes be involved. In particular, when multiple studies in a meta-analysis come from the same team of investigators (or their affiliates) and all of them find exactly the same conclusion, it is prudent to question and try to understand why so much evidence was generated by a single team. Science is an open global enterprise, and intense inbreeding may signal scientific fields in which one or a few stakeholders simply manipulate the published evidence according to their wishes and beliefs. In these cases, independence of the studies cannot be taken for granted and homogeneity, especially extreme homogeneity, may be a sign of major trouble for a meta-analysis rather than a reassurance of consistency.
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