PowerTOST crash-course [Design Issues]

posted by Helmut Homepage – Vienna, Austria, 2015-08-09 18:40 (3473 d 03:29 ago) – Posting: # 15199
Views: 11,356

Hi BE-proff,

❝ Looks like it is time for me to start learning R ;-)


Not necessary (here). Install [image] and package PowerTOST from one of the CRAN-mirrors. Then load the library by typing library(PowerTOST) in the R-console.
For an overview of available functions type help(package=PowerTOST) or for the one we are using here help(sampleN.TOST). The order of parameters is not important (here as given in my previous post); type:

sampleN.TOST(design="2x2", targetpower=0.9, alpha=0.05, theta1=0.8, theta2=1.25,
  theta0=1, CV=0.25, method="exact")

Will give:

+++++++++++ Equivalence test - TOST +++++++++++
            Sample size estimation
-----------------------------------------------
Study design:  2x2 crossover
log-transformed data (multiplicative model)

alpha = 0.05, target power = 0.9
BE margins        = 0.8 ... 1.25
Null (true) ratio = 1,  CV = 0.25

Sample size (total)
 n     power
28   0.902260

Some of the values are sampleN.TOST’s defaults (design="2x2", alpha=0.05, theta1=0.8, theta2=1.25, method="exact"). You get the same output with

sampleN.TOST(targetpower=0.9, theta0=1, CV=0.25)

For the approximations try method="noncentral" or method="shifted".
The most common settinge are targetpower=0.8 and theta0=0.95 (therefore, defaults as well). In such cases it is enough to type just:

sampleN.TOST(CV=0.20)

;-)

You can also directly copy/paste code which is posted here to the R-console. Saves time and avoids errors. You can paste the code to any text-file and save it with the extension .R
To execute it: In the R-console: File > Source R code…

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