Re: Comparing two variation coefficients

Reef Fish wrote:
Alfred wrote:
Thanks,

Here is a practical situation where it can be useful
to test for difference between two CV :

CV (also named "Relative Standard Deviation") is a recognized measure of
measurement repetability in Analytics. For instance, in can be used to
monitor drug tablet homogeneity (the so called "uniformity content test"
is a pre-requisite of the FDA for approval).

see : http://www.fda.gov/ora/compliance_ref/cpg/cpgdrg/cpg460-600.html

While it is true that the FDA used the term "relative standard
deviation",
but there is no indication that it meant CV!

Surely the statisticians in the FDA are not THAT statistically
challenged.
Or are they?

Is the FDA ignorant of the term Coefficient of Variation? If so, why
does it
use the ill-defined and undefined term "relative standard deviation"
repeatedly in the document? In particular it never even suggested
WHAT
the standards were.

So, how can you test if something meets the FDA standard if you don't
even know what the FDA is talking about?

-- Bob.


I'd never heard of the "relative standard deviation" either. But according to this glossary...

http://stats.oecd.org/glossary/detail.asp?ID=5061

it is another name for coefficient of variation. Here is the entry for "coefficient of variation".

----
Definition: The standard deviation of a random variable divided by the mean.

Context: Its dimensionless form makes it convenient for summarization.

The United States Bureau of Census alternatively refers to the coefficient of variation as the ratio of the standard error to the value being estimated, usually expressed in terms of a percentage. Also known as the relative standard deviation. (United States Bureau of Census, Glossary of Selected Abbreviations and Acronyms - refer http://eire.census.gov/cgi-bin/ssd/Glossary).

Source Publication: The International Statistical Institute, “The Oxford Dictionary of Statistical Terms”, edited by Yadolah Dodge, Oxford University Press, 2003.
----

The bit that perplexes me is how the Census Bureau can refer to the COV as the SE over the estimated value. Surely that should be SD, not SE.

--
Bruce Weaver
bweaver@xxxxxxxxxxxx
www.angelfire.com/wv/bwhomedir
.