4.16.24 21st Century Movements for Black Lives.pptx
Effect Size
1. Beyond p value: Effect Size April 4, 2008 Guy Lion
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4. Effect Size Measures Cohen’s d = (Mean Pilot – Mean Control )/Pooled Stand. Deviation Cohen’s d is similar to the unpaired t test t value. It relies on Standard Deviations instead of Standard Errors. Hedges’ g is a more accurate version of Cohen’s d Hedges’ Cohen’s d Adjustment for small sample
5. Pilots vs Controls In this example, there is a 1.9 Standard deviation difference between Pilots and Controls.
8. ES Confidence Interval The Effect Size standard deviation formula allows to build Confidence Intervals around Effect Size values.
9. 1 st Nonparametric test: Gamma Index Recalculated Gamma Index to make it the same sign as Cohen's d and Hedges' g.
10. 2 nd Nonparametric test: Cliff Delta Cliff Delta ranges between +1 when all values of one group are higher than the values of the other group and – 1 when reverse is true. Two overlapping distributions would have a Cliff Delta of 0.
12. Cliff Delta vs Cohen’s d If distributions are Normal, Cliff Delta = Percent of Nonoverlap within a Cohen's d framework.
13. Effect Size and Sample Size requirement The above formula results from the algebraic transformation of: t stat or Z value = Difference in Means/Group Standard Error.