R help - Nov 2005 - Coefficient of Variance (log values) !

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?

Thanks in Advance.

Regards,
Sharon

Sharon Anbu <sharonanandhi at 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.

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