Effect size is a way of quantifying the effectiveness of a particular intervention, relative to some comparison. It is the standardized mean difference between the two groups E (experimental) and C (control):
In studies where there is a large control group, its SD should be used in calculation of effect size. If there is not a true control group, or the control group is small, it is better to use a pooled estimate of SD:
, where NE and NC are the sizes of experimental and control groups, respectively.
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Updated at: 2015-07-27
Created at: 2014-02-06
Written by: Vesa Oikonen