Bioequivalence and Bioavailability Forum

Hi Imph,

❝ […] should we use the variance or the coefficient of variation? In Chow's paper (On Sample Size Calculation in Bioequivalence Trials, 2001) we see the variance in the formula on log-sclae while in his book (Design and Analysis of Bioavailability and Bioequivalence Studies, 2009) we see th coefficient of variation in the formula on log-scale.

Both are fine. From the ANOVA of the study’s data you get the residual variance. However, the CV is more common. If you use software, make sure to use the correct input. $$\eqalign{
CV&=\sqrt{\exp(s^2)-1}⁠\\
s^2&=\log_{e}(CV^2+1)
}$$ PS: If you want to perform the estimation manually, be aware that the formulas in Chow & Wang’s 2001 paper are only approximate and contain typos (I warned you already). See the errata: J Pharmacokinet Pharmacodyn. 2002; 29(2): 101-102.