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sizefx -- Calculate Cohen's d, Hedges' g, and the effect size (ES) correlation > (r)


sizefx varlist [if] [in]


sizefx computes Cohen's d, Hedges' g, and effect size (ES) correlations (r) for the two variables specified in varlist. The two variables specified correspond to the variables in a ttest, although the "==" operator is not used in the sizefx syntax.

The command displays Cohen's d statistic (Cohen 1988) using the pooled variance of the variables and Hedges' g statistic. The pooled variance for an unpaired t-test is used to calculate effect size even when using a dependent sample or correlated designs (Dunlap et al. 1996).

Additionally, it displays the effect size (ES) correlation (r) using the value of Cohen's d.


. sizefx age1 age2 . sizefx before after


Cohen, J. (1988) Statistical power analysis for the behavioral sciences, 2nd ed. Hillsdale, NJ: Lawrence Earlbaum Associates.

Dunlap, William P., Cortina, Jose M., Vaslow, Joel B., and Burke, Michael J. (1996) Meta-analysis of experiments with matched groups or repeated measures designs. Psychological Methods 1 no. 2, 170-177.

Thalheimer, W., and Cook, S. (2002, August) How to calculate effect sizes from published research articles: A simplified methodology. Retrieved 01 Apr 2010 from

Additional resources may be found at:

Links active as of 01 Apr 2010.


Matthew S. Openshaw, The University of Texas at Dallas, USA

Please send comments, suggestions or constructive criticism to the above email address.

sizefx v1.3 Update 01 Apr 2010