Hi Rick

The CV for a lognormal random variable is sqrt(exp(σ^2) – 1). Using the DIST=LOGNORMAL option on the PROC TTEST statement estimates this CV by sqrt(exp(s^2) – 1) rather than the usual sample CV. I notice that nowhere in the PROC TTEST documentation is the term GCV used - and rightly so in my opinion.

Kirkwood's definition of GCV = 100(GSD-1)% seems to be used to describe inter-laboratory and intra-laboratory variation in assay results in a number of academic publications.

Unlike the CV, Kirkwood's GCV was an attempt to describe variation about the geometric mean. He viewed it as an alternative to reporting the GSD. Instead of GSD = 2.14, GCV = 114% expresses how much to increase the GM by to get GM*GSD. Though searching for the phrases "geometric standard deviation" and "geometric coefficient of variation" on Google Scholar makes me think the GSD is a much more popular term than the GCV.

I am curious why you think "Kirkwood's GCV is not generally used. Instead, the accepted definition of the GCV is GCV = sqrt(exp(σ^2) – 1)”?