From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>

Date: Thu 01 Dec 2005 - 03:38:09 EST

Date: Thu 01 Dec 2005 - 03:38:09 EST

Sharon Anbu <sharonanandhi@gmail.com> writes:

*> Hi,
**>
*

> I am calculating coefficient of variance (CV) for my ELISA's data. For

*> normal values, I use the standard formula CV = SD/Mean * 100. Now, I
**> would like to calculate CV for log values. Can any one please
**> suggest me, how I can do this in R?
*

It usually makes best sense just to quote the SD of the natural-log transformed values as a coefficient of variation (sic). The precise formula is that in the lognormal distribution,

CV = sqrt(exp(SD^2)-1)

where CV is the coefficient of X and SD is the standard deviation of log(x). If you look at

curve(sqrt(exp(x^2)-1))

abline(0,1)

you'll see that the deviation is quite small for x < 0.3 or so.

-- O__ ---- Peter Dalgaard ุster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.htmlReceived on Thu Dec 01 04:28:56 2005

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