Sharon Anbu <[EMAIL PROTECTED]> 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 Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
