Bioequivalence and Bioavailability Forum • Initial sample size guess for the Potvin methods

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

posted by Helmut – Vienna, Austria, 2017-08-19 19:12 (2864 d 04:50 ago) – Posting: # 17712
Views: 30,182

Hi ElMaestro,

❝ 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.

I see.

So with your code I end up with 10/seq or 20 in stage 1. That’s actually the sample size of the fixed design. Try this (ASN is the expected average total sample size, pwr is the probability to show BE in stage 1 or 2, stop the chance to end if stage 1, and pct.stg2 the percentage of studies proceeding to stage 2):

library(PowerTOST) library(Power2Stage) CV <- 0.2 GMR <- 0.95 target <- 0.8 n.fix <- sampleN.TOST(CV=CV, theta0=GMR, targetpower=target, details=FALSE, print=FALSE)[["Sample size"]] n1 <- seq(12, n.fix, 2) res <- data.frame(CV=CV, GMR=GMR, target=target, n1=n1, ASN=NA, pwr.1=NA, stop=NA, pct.stg2=NA, pwr.2=NA) for (j in seq_along(n1)) { x <- power.2stage(CV=CV, theta0=GMR, targetpower=target, n1=n1[j], details=FALSE) res[j, "ASN"] <- x[["nmean"]] res[j, "pwr.1"] <- x[["pBE_s1"]] res[j, "stop"] <- 100-x[["pct_s2"]] res[j, "pct.stg2"] <- x[["pct_s2"]] res[j, "pwr.2"] <- x[["pBE"]] } print(signif(res, 3), row.names=FALSE) CV GMR target n1 ASN pwr.1 stop pct.stg2 pwr.2 0.2 0.95 0.8 12 20.6 0.413 43.7 56.3 0.842 0.2 0.95 0.8 14 20.0 0.527 55.8 44.2 0.848 0.2 0.95 0.8 16 20.0 0.619 66.1 33.9 0.851 0.2 0.95 0.8 18 20.6 0.695 74.6 25.4 0.856 0.2 0.95 0.8 20 21.7 0.752 81.5 18.5 0.862

I still prefer 16 subjects in stage 1 (already ~62% power and a ~66% chance to stop). The final power is similar to your n1 20 but ASN is lower.

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Complete thread:

Initial sample size guess for the Potvin methods ElMaestro 2017-08-19 15:04
- Initial sample size guess for the Potvin methods Helmut 2017-08-19 16:06
  - Initial sample size guess for the Potvin methods ElMaestro 2017-08-19 16:14
    - Initial sample size guess for the Potvin methodsHelmut 2017-08-19 17:12
      - Initial sample size guess for the Potvin methods ElMaestro 2017-08-19 17:17
        
        Confuse-a-Cat Helmut 2017-08-19 17:33
        
        Confuse-a-Cat ElMaestro 2017-08-19 17:56
    - loop ↔ vectorized ↔ direct Helmut 2017-08-20 14:40
      - loop ↔ vectorized ↔ direct ElMaestro 2017-08-20 15:22
        
        loop ↔ vectorized ↔ direct Helmut 2017-08-20 16:23
        
        loop ↔ vectorized ↔ direct ElMaestro 2017-08-20 17:22
- The n ext crackpot iteration ElMaestro 2017-08-19 20:04
  - The n ext crackpot iteration Helmut 2017-08-20 02:20
- The ultimate crackpot iteration! ElMaestro 2017-08-20 14:35
  - The ultimate crackpot iteration! Helmut 2017-08-20 15:11
    - The ultimate crackpot iteration! ElMaestro 2017-08-20 15:28
      - The ultimate crackpot iteration! Helmut 2017-08-20 16:06
        
        The ultimate crackpot iteration! ElMaestro 2017-08-20 16:15
        
        The ultimate crackpot iteration! Helmut 2017-08-20 18:58
        
        The ultimate crackpot iteration! ElMaestro 2017-08-20 19:32
        
        Suggested code ElMaestro 2017-08-21 18:13
        
        Nitpicker! Helmut 2017-08-22 13:33
        
        Nitpicker! ElMaestro 2017-08-22 17:27
        
        Nitpicker! Helmut 2017-08-22 17:49
        
        Nitpicker! ElMaestro 2017-08-22 17:59
        
        Nitpicker! Helmut 2017-08-22 19:15
        
        Benchmark code ElMaestro 2017-08-22 22:29
        
        Benchmark code Helmut 2017-08-23 01:48