A user friendly effect size--When normality matters

Authors

Glenn T. Waterbury, James Madison University
Christine E. DeMarsFollow

Publication Date

2019

Document Type

Article

Abstract

There is a need for effect sizes that are readily interpretable by a broad audience. One index that might fill this need is π, which represents the proportion of scores in one group that exceed the mean of another group. The robustness of estimates of π to violations of normality had not been explored. Using simulated data, three estimates of π (π_Direct , r, and r_robust) were studied under varying conditions of sample size, distribution shape, and group mean difference. This study demonstrated that r and r_robust were biased estimates of π when data were non-normal. We recommend that neither be used in estimating π unless data are normally distributed.

Creative Commons License

This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Recommended Citation

Waterbury, G. T., & DeMars, C. E. (2019). (Brief Research Report): A user friendly effect size--When normality matters. Journal of Experimental Education, 87, 260-268. https://doi.org/ 10.1080/00220973.2018.1434757