Cohens Sample Size. Sp is the pooled standard deviation. If M1 is bigger than M2 your effect size will be positive.
Cohens d is the appropriate effect size measure if two groups have similar standard deviations and are of the same size. To detect an r5 using with a two-tailed α 01 at 80 power I need 41 participants. M2 and M1 are the means.
Small medium or large.
We now show how to calculate the sample size requirements in the case where there are only two rating categories. M2 and M1 are the means. S1 and S2 are the standard deviations. Effect sizes below 02 are regarded as small 03-05 are regarded as medium and 08 is regarded as large.
