Effect size

Effect size is an index that allows estimation of strength of an effect across studies which use different measures. It is based on the paired standard deviation of the control and experimental group, and thus can be read as a standard deviation index ranging from zero to 1 or more, with 0.2 considered to be small, 0.4 to be medium, and 0.7 to be large. However, depending on study design and characteristics, effect sizes as low as 0.1 may be educationally meaningful.