Effect sizes for experimenting psychologists

Can J Exp Psychol. 2003 Sep;57(3):221-37. doi: 10.1037/h0087427.


This article describes three families of effect size estimators and their use in situations of general and specific interest to experimenting psychologists. The situations discussed include both between- and within-group (repeated measures) designs. Also described is the counternull statistic, which is useful in preventing common errors of interpretation in null hypothesis significance testing. The emphasis is on correlation (r-type) effect size indicators, but a wide variety of difference-type and ratio-type effect size estimators are also described.

MeSH terms

  • Humans
  • Models, Psychological*
  • Psychology, Experimental / methods*
  • Psychology, Experimental / statistics & numerical data*