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J Exp Psychol Gen. 2016 May;145(5):643-654. doi: 10.1037/xge0000159. Epub 2016 Mar 28.

Meta-analysis to integrate effect sizes within an article: Possible misuse and Type I error inflation.

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Department of Psychology, University of Reading.


In recent years an increasing number of articles have employed meta-analysis to integrate effect sizes of researchers' own series of studies within a single article ("internal meta-analysis"). Although this approach has the obvious advantage of obtaining narrower confidence intervals, we show that it could inadvertently inflate false-positive rates if researchers are motivated to use internal meta-analysis in order to obtain a significant overall effect. Specifically, if one decides whether to stop or continue a further replication experiment depending on the significance of the results in an internal meta-analysis, false-positive rates would increase beyond the nominal level. We conducted a set of Monte Carlo simulations to demonstrate our argument, and provided a literature review to gauge awareness and prevalence of this issue. Furthermore, we made several recommendations when using internal meta-analysis to make a judgment on statistical significance.

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