Hi, I am trying to obtain bootstrap parameter estimates from a PKPD model. I have runned the bootstrap and it works fine. However, I havent been able to stratify my bootstrap. In my bootstrap estimates, I would like to have “GROUP” as covariate but when the software doesnt allow me to stratify my bootstrap. “GROUP” is a covariate in the text file. The covariate is in text format. I tried to use a numerical covariate as well but neither does that work. See caption from text file below. In the attached figure you can see how it looks when I try to select stratification. I currently use Phoenix WinNonlin 6.2 and NLME 1.1. What is missing here to do a stratified bootstrap? Kind regards, Rasmus test(){ covariate(tvKa, tvV1,tvCL,tvCLD,tvVd,Salt,Bio,GROUP) # PK deriv(Aa = - tvKa * Aa) deriv(A1 = tvKaAa - tvCLC- tvCLDC +tvCLDC2) deriv(A2 = tvCLDC - tvCLDC2) #Disease model deriv(E = Rate* (1-(1*C/(IC50+C)))) 
