## Problems with PASS [Software]

Dear Helmut, dear ElMaestro,

» » I could be wrong but...
»
» We all may be but…

Me too. Especially me .

Just my 2 cents.
Differences between PASS and PowerTOST w.r.t replicate cross-over designs
• PASS uses degrees of freedom from an cross-over ANOVA having a carry-over term
PowerTOST uses only the usual terms tmt, period, sequence and subject
• The design constant for the 2x2x4 design is 1.1 instead of 1.0 in PowerTOST
• The power is calculated approximately in PASS via the shifted central t-distribution
• For log-transformed data the approximation CV ~ se is used in PASS (!).
se is the standard error of the residuals.

Especially the last feature is due to the differences in the sample sizes got from PASS compared to. My recommendations supporting Helmut's recommendations above:
Don't use the sample sizes for replicate designs obtained by PASS because
• They rely on statistics not used in the evaluation of the study
• They rely on crude approximations, especially on CV ~ se which may work for small CVs but is beyond repair for higher values

Regards,

Detlew

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