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Calculators

##
Effect Size Calculators

Calculate* *Cohen's *d* and the effect-size correlation, *r*_{Yl}*, *using --

For a discussion of these effect size measures see Effect Size Lecture Notes

## Calculate *d* and *r* using means and standard deviations

Calculate the value of Cohen's

*d*and the effect-size correlation,*r*_{Yl}, using the means and standard deviations of two groups (treatment and control).Cohen's* d* = *M*_{1} - *M*_{2} / s_{pooled}

where s_{pooled} =√[(s _{1}^{2}+ s _{2}^{2}) / 2]

r_{Yl} = d / √(d^{2} + 4)

Note: d and r_{Yl }are positive if the mean difference is in the predicted direction.

## Calculate *d* and *r* using *t* values and *df* (separate groups *t* test)

Calculate the value of Cohen's

*d*and the effect size correlation, r_{Yl}, using the*t*test value for a between subjects*t*test and the degrees of freedom.Cohen's* d* = 2*t* /√(*df*)

r_{Yl} = √(*t ^{2} / (t^{2} + df))*

Note: d and r_{Yl }are positive if the mean difference is in the predicted direction.

**Warning: Do not use a paired t-test value when computing effect sizes.** See Effect Size Lecture Notes.

revised - 03/20/00 © 1998, 1999 Lee A. Becker