- Thread starter Buckeye
- Start date

If the difference in means is statistically significant, you may quantify the effect size with Cohen's D or R-square. This would help in addressing the effect size issue that @katxt mentioned.

N = ((Z * sigma)/E)^2 where Z is the appropriate quantile for a given alpha level. E is the desired margin of error. This formula does not take into account power. Can someone elaborate on this formula?