Loss in power [Regulatives / Guidelines]

posted by Helmut Homepage – Vienna, Austria, 2017-05-06 19:31 (2214 d 02:00 ago) – Posting: # 17310
Views: 29,075

Hi mittyri and all,

R-code to estimate the loss in power (two groups of equal size). Example for my simulations above and assuming that we will get a significant Group-by-Treatment interaction at the level of the test.

library(PowerTOST)
CV          <- 0.3
theta0      <- 1
targetpower <- 0.8
p.level     <- 0.1
res         <- sampleN.TOST(CV=CV, theta0=theta0, targetpower=targetpower,
                            print=FALSE)
N           <- res[["Sample size"]]
if (N >= 12) { # at least minimum sample size acc. to GLs?
  pwr.mod3pooled <- res[["Achieved power"]]
} else {
  N <- 12
  pwr.mod3pooled <- power.TOST(CV=CV, theta0=theta0, n=N)
}
pwr.mod2       <- suppressMessages(power.TOST(CV=CV, theta0=theta0,
                                              n=N-1)*(1-p.level))
pwr.mod3groups <- power.TOST(CV=CV, theta0=theta0, n=N/2)*p.level
pwr.mod2and3   <- pwr.mod2+pwr.mod3groups
cat(sprintf("CV %5.3f%%, theta0 %.4f, targetpower %.2f%%    : sample size %i",
            100*CV, theta0, 100*targetpower, N),
    "\nLevel of the G\u00D7T test (model 1)                  :",
      sprintf("% 6.4f", p.level),
     "\nPower of studies evaluated by model 2 (pooled)   :",
      sprintf("%5.2f%%", 100*pwr.mod2),
    "\nPower of studies evaluated by model 3 (groups)   :",
      sprintf("%5.2f%%", 100*pwr.mod3groups),
    "\nModel 2 (pooled) and 3 (groups) combined         :",
      sprintf("%5.2f%%", 100*pwr.mod2and3),
    "\nPower of studies evaluated by model 3 (pooled)   :",
      sprintf("%5.2f%%", 100*pwr.mod3pooled),
    "\nLoss in power if simple model 3 cannot be applied:",
      sprintf("%5.2f%%", 100*(pwr.mod3pooled-pwr.mod2and3)), "\n")

Gives

CV 30.000%, theta0 1.0000, targetpower 80.00%    : sample size 32
Level of the G×T test (model 1)                  :  0.1000
Power of studies evaluated by model 2 (pooled)   : 71.80%
Power of studies evaluated by model 3 (groups)   :  3.25%
Model 2 (pooled) and 3 (groups) combined         : 75.05%
Power of studies evaluated by model 3 (pooled)   : 81.52%
Loss in power if simple model 3 cannot be applied:  6.47%

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