[R] "CV" for log normal data

Terry Therneau therneau at mayo.edu
Wed Feb 22 15:08:52 CET 2012

If a variable y has (approximately) constant CV, then log(y) has
(approximately) constant variance.  So, use the standard deviation of
the data.

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Hi, I have a microarray dataset from Agilent chips. The data were really
log ratio between test samples and a universal reference RNA. Because of
the nature of log ratios, coefficient of variation (CV) doesn't really
apply to this kind of data due to the fact that mean of log ratio is
very close to 0. What kind of measurements would people use to measure
the dispersion so that I can compare across genes on the chip to find
stably expressed genes? something similar to CV would be easily

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