Bioequivalence and Bioavailability Forum

maximum sample size at which CV? [🇷 for BE/BA]

posted by Helmut  – Vienna, Austria, 2016-01-26 17:31 (3433 d 06:27 ago) – Posting: # 15856
Views: 18,271

Dear Shuanghe,

adding a few lines of code to what Detlew wrote.

library(PowerTOST)
GMR <- seq(0.82, 0.95, 0.005)
CV  <- seq(0.25, 0.35, 0.005)
n   <- matrix(nrow=length(CV), ncol=length(GMR), byrow=TRUE,
              dimnames=list(CV, GMR))
pwr <- n
for (j in seq_along(CV)) {
  for (k in seq_along(GMR)) {
    x <- sampleN.RSABE(CV=CV[j], theta0=GMR[k],
                       design="2x2x4", print=FALSE,
                       details=FALSE)
    if (is.na(x[["Sample size"]])) { # 2nd try if necessary
      x <- sampleN.RSABE(CV=CV[j], theta0=GMR[k],
                         design="2x2x4", print=FALSE,
                         details=FALSE, nstart=x[["nlast"]])
    }
    n[j, k]   <- x[["Sample size"]]
    pwr[j, k] <- x[["Achieved power"]]
  }
}
print(n)
print(pwr)
max.n   <- apply(n, 2, max)     # maximum n for each GMR
min.pwr <- vector()             # explore min. power
for (k in seq_along(GMR)) {
  x <- n[, k]
  y <- which(x == max.n[k]) # max. sample size(s)
  if (length(y) == 1) { # already there
    min.pwr[k] <- names(y)
  } else {              # pick the minimum
    min.pwr[k] <- names(which(pwr[y, k] == min(pwr[y, k])))
  }
}
min.pwr <- as.numeric(min.pwr)
shift   <- diff(range(GMR))*0.01
plot(GMR, min.pwr, type="p", ylim=range(CV),
  ylab="CV for maximum n", las=1)
abline(h=0.3, lty=3)
text(GMR-shift, min.pwr, labels=max.n,
  cex=0.9, srt=90, pos=1, offset=1.6)

The maximum sample size within each GMR-column shows this strange behavior due the FDA’s combination of the regulatory constant log(1.25)/0.25, the PE-restriction, and the discontinuity (since RSABE can only be applied if CV_wR ≥0.30). In the n-matrix you find the same maximum sample sizes in some GMR-columns. As Detlew pointed out, you can look at the minimum power to decide which one to select.


Interesting shape!

—
Dif-tor heh smusma 🖖🏼 Довге життя Україна! 
Helmut Schütz


The quality of responses received is directly proportional to the quality of the question asked. 🚮
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Complete thread:

• PowerTOST sample size FDA full replicate T/R ratio at 85% Shuanghe 2016-01-25 17:49 
  • PowerTOST sample size FDA full replicate T/R ratio at 85% d_labes 2016-01-26 12:05
    • PowerTOST sample size FDA full replicate T/R ratio at 85% Shuanghe 2016-01-26 12:55
      • PowerTOST sample size FDA full replicate T/R ratio at 85% d_labes 2016-01-26 14:07
      • maximum sample size at which CV?Helmut 2016-01-26 16:31
        • maximum sample size at which CV? nobody 2016-01-26 17:40
        • maximum sample size at which CV? d_labes 2016-01-27 08:41
          • maximum sample size at which CV? nobody 2016-01-27 09:08
            • OT: Stop - think -act d_labes 2016-01-27 09:31
        • maximum sample size at which CV? Shuanghe 2016-01-28 12:44
          • target power 90% Helmut 2016-01-28 13:49
            • PowerTOST update d_labes 2016-02-01 19:16
              • #1,000 Helmut 2016-02-01 21:49
                • OT: post #1,000 d_labes 2016-02-02 21:17
                • #1,000 ElMaestro 2016-02-03 16:32
                  • #1,000 Helmut 2016-02-03 16:50
                  • OT: #1,000 d_labes 2016-02-05 15:50
                    • OT: #1,000 ElMaestro 2016-02-05 17:02
                      • OT: #1,000 d_labes 2016-02-05 19:48
                        • OT: #1,000 ElMaestro 2016-02-06 15:45
                          • OT: #1,000 nobody 2016-02-07 09:50