Cohen's d

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A measure of effect size, the most familiar form being the difference between two means (M1 and M2) expressed in units of standard deviations: the formula is d = (M1M2)/σ, where σ is the pooled standard deviation of the scores in both groups. A value of d below 0.20 is considered small, 0.50 medium, and 0.80 large. [Named after the US psychologist Jacob (Jack) Cohen (1923–98) who devised it and popularized it in his book Statistical Power Analysis for the Behavioral Sciences (1969, 1988)]

Subjects: Psychology.

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