On 1 Mar 2000 15:31:45 GMT, [EMAIL PROTECTED] (Raghuramaiah
Gompa) wrote:
>
> How would you calculate the standard deviation of a ratio?
>
> i.e. We have:
>
> Nt � SD (population at time t; mean � SD)
> N0 � SD (population at time 0; mean � SD)
>
> Survival ratio at time t = Nt/N0
>
> Is there any way to have a confidence interval on the ratio?
>
> This is a standard measurement in microbiology but
> none seems to address its statistical validity. Any ideas?
...
It seems to have been a discussed pretty well, long ago. I see your
answer, in DJ Finney's classic textbook, Statistical Method in
Biological Assay, (1971) pages 28-29. He gives the formulas that
come from Fieller's theorem, for "assigning fiducial limits to a ratio
of two means...." His reference for Fieller is (1940) "The
biological standardization of insulin"; Journal of the Royal
Statistical Society, Supplement, 7: 1-64.
It is rather complicated, but it simplifies a lot if the denominator
is large compared to its standard error; and it simplifies even more
if the observations of numerator and denominator are independent.
--
Rich Ulrich, [EMAIL PROTECTED]
http://www.pitt.edu/~wpilib/index.html
===========================================================================
This list is open to everyone. Occasionally, less thoughtful
people send inappropriate messages. Please DO NOT COMPLAIN TO
THE POSTMASTER about these messages because the postmaster has no
way of controlling them, and excessive complaints will result in
termination of the list.
For information about this list, including information about the
problem of inappropriate messages and information about how to
unsubscribe, please see the web page at
http://jse.stat.ncsu.edu/
===========================================================================
