In meta-analytic studies where one wishes to estimate magnitude of effects based on multiple investigations, it is important to recognize that Kendall's Tau, often considered equivalent to Spearman's Rho as an ordinal measure of correlation, in fact has a different metric. This article reviews formulae for converting Tau to Rho, Pearson's r, r2, Fisher's Zr, and Cohen's standardized range of means index of effect size, as well as presents a table of the values corresponding to Tau coefficients from 0 through 1.
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