You are designing a study to be evaluated with a two-sample nondirectional independent t test at a = .05. You want .90 power. You expect Cohenâ€™s d to be about .40. How many subjects will you need peer group?

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j=d*sqrt(n/2)

where j is the power of the test

d is the cohen's d

n is the sample size per group

0.9=0.4 sqrt(n/2)

0.81=0.16n/2

1.62=0.16n

n=10

the number of subjects is 10 per sample

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