Effect Size Calculator for T-Test
For the independent samples T-test, Cohen's d is determined by calculating
the mean difference between your two groups, and then dividing the result by the
pooled standard deviation.
Cohen's d = (M_{2} -
M_{1}) ⁄ SD_{pooled}
where:
SD_{pooled} = √((SD_{1}^{2} + SD_{2}^{2})
⁄ 2)
Glass' Delta and Hedges' G
Cohen's d is the appropriate effect size measure if two groups have similar
standard deviations and are of the same size. Glass' delta, which uses
only the standard deviation of the control group, is an alternative measure if each
group has a different standard deviation. Hedges' g, which provides a
measure of effect size weighted according to the relative size of each sample, is
an alternative where there are different sample sizes. (This is important! If you've got different sample sizes then you should use Hedges' g.)
Enter Your Values
Please enter the sample mean (M), sample standard deviation (s)
and sample size (n) for each group. Two things to note: (1) if you intend
to report Glass's delta, then you need to enter your control group
values as Group 1; and (2) if you don't provide values for n,
the calculator will still calculate Cohen's d and Glass' delta,
but it won't generate a value for Hedges's g.
Please enter your values in the boxes above, and press the "Calculate" button.
Cohen's d: Not yet calculated
Glass' delta: Not yet calculated
Hedges' g: Not yet calculated