Bioequivalence and Bioavailability Forum

Dear Helmut,

❝ Yep. BTW, mean plots (I hope you are using geometric means) are not relevant in BE – they give just a first impression.

If mean curves are not relevant (full ACK with this statement ) but only an illustration why should the type of mean matter? IMHO the arithmetic means (mostly much easier to obtain via built in functions, SAS f.i. doesn't have a function for the geomean) will do also.
Of course you are right from a 'theoretical' point of view. The geomean is more appropriate if one presumes a log-normal distribution for the concentrations. But an Austrian friend of mine is not totally convinced of that .

What to do with values <LLOQ in calculating the geometric means? Setting to zero as usual would result in geomean=0 if any value at the considered time point is <LLOQ, according to the definition
geomean=n-th root of the product of the values

But usually the geomean is calculated via logs. And if I remember a quite recent discussion correct WNL/Phoenix will produce silently missings, like my SAS beast also. That corresponds to "leave values <LLOQ out".
Only R which treats log(0) = -Inf comes natively out with geomean=0 if calculated via mean of logs and then back-transformed.

Using the geomean may further require different strategies for handling <LLOQ values depending on the time point. We had a discussion about this here back in the year 2008.