Bioequivalence and Bioavailability Forum

Dea-maidin Angus!

❝ I have the program WinNonlin…

Forget it (will tell you later why).

❝ …and another program that does ANOVA (NCSS)

OK, could do the job.

❝ I believe I need to have the inter-subject variance of the PK paramater.

Nope. You have the total variance. See this post.

❝ I use the LN values of the PK paramater. So I think a one way ANOVA is appropriate and what is the correct name of the inter subject variance paramater given by the ANOVA output?

Haven’t used NCSS for years. Maybe residual variance?

❝ I am on the LN scale so I think I take the square root of the intersubject variance paramater and multiply by 100 to get the CV as percentage.

That’s an approximation. Use \(100\sqrt{e^{MSE}-1}\) like you would do in a Xover.

❝ Please can I be advised of the terminology and if I am doing the correct calculation.

If you using the formula above, no problem. Now a warning (see this presentation; some more stuff here). Though the t-test is fairly robust if the two groups show unequal variances, it is sensitive against imbalance.^* The outcome will be liberal (CI too narrow).
So you asked one question (the CV) and get another answer: WinNonlin (up to the latest release of Phoenix 6.3) gives the CI based on the t-test for equal variances – even if you select “Satterthwaite degrees of freedom” in the options. That’s a bug. Search the forum for some background information.

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• In your case with 12/12 per group no big deal. But use the right model. Follow FDA’s guidance.