Guide to calculating, interpreting and using effect size

Cohen describes an effect size of 0.8 as ‘grossly perceptible and therefore large’ and equates it to the difference between the heights of 13 year old and 18 year old girls. As a further example he states that the difference in IQ between holders of the Ph.D. degree and ‘typical college freshmen’ is comparable to an effect size of 0.8. ................
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