Paired ttest  

Find sample size: If you know the mean difference and its standard deviation, use this form to find the number of subjects you need. 
Find effect size: If you know the number of subjects and the standard deviation of the change, use this form to find how small a difference you can detect. 
* If you don't know the SD of the difference


Choose another study design Contact: sfh2@columbia.edu Source: G.W. Snedecor & W.G. Cochran Statistical Methods (7th ed., p. 104) 