## Initial sample size guess for the Potvin methods [Two-Stage / GS Designs]

Hi Hötzi,

» Error in Power.calc(nps1, GMR, CV, Is.St2 = 1) :  »   could not find function "Power.calc"
» Did I specify the arguments wrongly?

That's why I included the remark:
##equation in Potvin et al.
I thought you'd be plugging in your own, but be that as it may.

An implementation of the function is here:

alpha1=0.0294 alpha2=0.05 vecQT1=c(1:5000) vecQT2=c(1:5000) for (i in 1:5000)    {     vecQT1[i]=qt(p=1-alpha1, df=i)     vecQT2[i]=qt(p=1-alpha2, df=i)    } Power.calc=function(Nps, GMR, CV, Is.St2=0) {   s=sqrt(log(1+CV*CV))   nom1=log(1.25/GMR)   nom2=-log(1.25*GMR)   den=s*sqrt(2/(2*Nps))   df=Nps*2-2   if (Is.St2==T) df=df-1   ##cat("1-a=", 1-alpha, "df=",df,"\n")   if (Is.St2==0) q=vecQT1[df]     else         q=vecQT2[df]   pw=pt( (nom1/den) -q, df) - pt( (nom2/den) +q, df)   if (pw<0) pw=0.01   return(pw) }

Edit: Forgot to write: For classical B the alphas are (0.0294, 0.0294) and for C they are (0.05, 0.0294) though that isn't related to the topic. Second, Hötzi, you gave a little table which I am not very sure how to read. Note this isn't about the sample size calculation itself, this is about the initial guess used for the sample size calculation by up/down iteration.

Pass or fail!
ElMaestro