Rooyesh-e- Ravanshenasi Journal(RRJ)

Dissatisfaction with tests of statistical significance in last decades has led to emergence of effect size measures. Effect size is generally a measure, incorporated into statistical analyses in order to emphasize the size of the difference rather than sample size. Assessing and reporting measures of effect size are of absolute importance in behavioral sciences and American Psychological Association encourages researchers to report them. This paper investigates the concept and pertaining calculations of effect size measures. Moreover, the necessity of reporting measures of effect size in research articles has been elaborated. A number of alternative measures of effect size were described. Finally, advice on the use of effect sizes in meta-analysis is summarized