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Effect size is a statistical index that refers to the degree of relationship between two variables or the magnitude of an effect. It can be calculated as a generic statistic for change in the absence of treatment from pretest to posttest for a single group, or include treatment effects based on two or more groups. Effect size is a standard part of much statistical reporting in education economics and finance. Whether researchers develop indicators of teacher effectiveness or analyze impacts of educational resources on student outcomes, effect size is an important tool in interpreting study findings. Because different studies employ different outcome measures with different metrics, effect size estimates are used to convert diverse measures into the common metric, allowing studies to be compared, combined, ...

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