Effect Size

"Statistical significance only tells the researcher how likely it is that an observed finding could have occurred by chance. It does not say anything about magnitude of the effect observed. Effect size is a name given to a group of statistics that measure the magnitude of a treatment effect. In many cases, effect size is a better measure of research outcomes than the significance level. This is because with large samples, one can observe statistically significant group differences even when only a tiny effect is present. Unlike significance tests, effect size indices are independent of sample size." source: http://www.umdnj.edu/idsweb/shared/effect_size.htm

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