Study costs: Replicate seems to be cheaper [Regulatives / Guidelines]

posted by Helmut Homepage – Vienna, Austria, 2017-03-21 15:50 (2554 d 11:55 ago) – Posting: # 17176
Views: 23,074

Hi Dan,

I agree with VStus.

❝ For your calculation please keep in mind: the more study periods you have the higher the risk of drop outs.


As I wrote above:

❝ ❝ I would not be worried about the higher chance of dropouts in the replicate study. The impact on power is low (unless the drug is nasty and dropouts are caused by AEs).


Try:

library(PowerTOST)
CV  <- 0.31
dor <- 5 # dropout-rate (in each washout) in percent
des <- "2x2x2"
res <- sampleN.TOST(CV=0.31, design=des, print=FALSE)
n   <- res[["Sample size"]]
pwr <- res[["Achieved power"]]
wo  <- as.integer(substr(des, nchar(des), nchar(des)))-1
el  <- n # eligible subjects
for (j in 1:wo) {
  el <- el*(1-dor/100)
}
cat("Study started with", n, "subjects (expected power",
    sprintf("%.1f%%).", 100*pwr),
    "\nStudy ended with", as.integer(el), "eligible subjects (expected power",
    sprintf("%.1f%%).", 100*power.TOST(CV=CV, design=des, n=el)), "\n")
# Study started with 42 subjects (expected power 81.1%).
# Study ended with 39 eligible subjects (expected power 79.2%).

des <- "2x2x4"
res <- sampleN.TOST(CV=0.31, design=des, print=FALSE)
n   <- res[["Sample size"]]
pwr <- res[["Achieved power"]]
wo  <- as.integer(substr(des, nchar(des), nchar(des)))-1
el  <- n
for (j in 1:wo) {
  el <- el*(1-dor/100)
}
cat("Study started with", n, "subjects (expected power",
    sprintf("%.1f%%).", 100*pwr),
    "\nStudy ended with", as.integer(el), "eligible subjects (expected power",
    sprintf("%.1f%%).", 100*power.TOST(CV=CV, design=des, n=el)), "\n")
# Study started with 22 subjects (expected power 83.3%).
# Study ended with 18 eligible subjects (expected power 75.1%).

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