I am running a Wilcoxon-signed rank test, and as suggested by King et al., the best effect size to report for this analysis would be the matched-pairs rank biserial correlation.

How is the power (1-B) calculated based on this effect size?

The package "pwr" in R allows calculating the power based on linear correlation coefficients (i.e., Pearson correlation coefficient, "r"). Yet, the matched-pairs rank biserial correlation is very close to the Pearson correlation coefficient. Could I use the latter coefficient in the pwr.r.test() function in R?

Another way would be to use the G*Power software by selecting "t-tests" in the Test Family selection menu and then by selecting "Correlation: Point biserial model" in the Statistical test selection menu. Would this be correct?

Thanks in advance!

King, B. M., Rosopa, P. J., & Minium, E. W. (2018). Statistical reasoning in the behavioral sciences. John Wiley & Sons, 383-384.

  • $\begingroup$ Perhaps you could calculate power for a paired t-test. In most cases, the Wilcoxon signed-rank test is more powerful, so this would give you a somewhat conservative estimate for power. $\endgroup$
    – num_39
    Mar 15, 2022 at 6:18
  • $\begingroup$ Thank you for your answer :) Yes, that would be one way, however, to calculate it for paired t-tests I would need to use Cohen's-dz which it is not the most appropriate effect-size for non-parametric tests. But as long as I report the limitation it may be good, thanks! $\endgroup$
    – Sara Coppi
    Mar 16, 2022 at 9:27
  • $\begingroup$ The problem here is trying to estimate power without any knowledge of the parameters. If you know something about the parameters, then you have some options. See this answer: stats.stackexchange.com/questions/521477/… $\endgroup$
    – num_39
    Mar 16, 2022 at 9:55


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