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A Critique and Improvement of the CL Common Language Effect Size Statistics of McGraw and Wong

Department o f Experimental Psychology, ELTE, Hungary

Harold D. Delaney

Department of Psychology, UNM, U.S.A

McGraw and Wong (1992) described an appealing index of effect size, called CL, which measures the difference between two populations in terms of the probability that a score sampled at random from the first population will be greater than a score sampled at random from the second. McGraw and Wong introduced this "common language effect size statistic" for normal distributions and then proposed an approximate estimation for any continuous distribution. In addition, they generalized CL to the n-group case, the correlated samples case, and the discrete values case.

In the current paper a different generalization of CL, called the A measure of stochastic superiority, is proposed, which may be directly applied for any discrete or continuous variable that is at least ordinally scaled. Exact methods for point and interval estimation as well as the significance tests of the A = .5 hypothesis are provided. New generalizations ofCL are provided for the multi-group and correlated samples cases.

Key Words: group comparison • effect size measures • measure of stochastic superiority • stochastic equality • stochastic homogeneity • Mann-Whitney-Wilcoxon test • Kruskal-Wallis test • Sign-test • Friedman test

Journal of Educational and Behavioral Statistics, Vol. 25, No. 2, 101-132 (2000)
DOI: 10.3102/10769986025002101


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