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Function CVpooled (package PowerTOST) [R for BE/BA]

posted by Elena777 - Belarus, 2018-01-21 08:53  - Posting: # 18238
Views: 7,164

Dear all! I am new to R and RStudio. It will be very useful to me if you help me with the following questions:

1. Here is an example of my data:

CVs <- ("
 PKmetric | CV     | n  |design|source   
    Cmax  | 0.2617 | 23 | 2x2  | study 1
    Cmax  | 0.1216 | 24 | 2x2  | study 2
    Cmax  | 0.1426 | 24 | 2x2  | study 3
    Cmax  | 0.1480 | 27 | 3x3  | study 4
    Cmax  | 0.1476 | 27 | 3x3  | study 4a 
    Cmax  | 0.2114 | 18 | 2x2  | study 5

")
txtcon <- textConnection(CVs)
CVdata <- read.table(txtcon, header=TRUE, sep="|", strip.white=TRUE, as.is=TRUE)
close(txtcon)

CVsCmax <- subset(CVdata, PKmetric=="Cmax")
CVpooled(CVsCmax, alpha=0.2, logscale=TRUE)

print(CVpooled(CVsCmax, alpha=0.2, robust=TRUE), digits=6, verbose=TRUE)


The result I got:

CVpooled(CVsCmax, alpha=0.2, logscale=TRUE)
0.1677 with 181 degrees of freedom
 
print(CVpooled(CVsCmax, alpha=0.2, robust=TRUE), digits=6, verbose=TRUE)
Pooled CV = 0.175054 with 129 degrees of freedom (robust df's)
Upper 80% confidence limit of CV = 0.185309


Why are degrees of freedom so huge? And why did I get two different results 0.1677 and 0.1750? Is it acceptable and can I use any result to calculate sample size in PowerTOST? What result must I choose (0.1677, 0.1750, 0.1853) for calculating sample size?

2. And the second question. Is argument "digits" from function CVpooled simply a number of observations for a variable?

Thank you in advance!

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