Nick's suggestion sounds very much worth looking into. I don't have
timely
access to the book, but from what's said about it (Google for "Re:
Confidence Interval on Quotient" and "Rolf Turner"), it bears a
striking
resemblance to Fieller's methods.
I've requested it on interlibrary loan. I'll scan the chapter and
convert to PDF and send if I get it if you like. Thanks for the
reference, Nick.
If John McCloskey and his audience don't mind working with transformed
values, then a simple approach to the pharmacologist's 'fold above
control'
penchant is to logarithmically transform the fluorescence values and
submit
them to ordinary least squares regression with a dummy (indicator)
variable
for the control group (0) and drug group (1). The Student's t-based
confidence interval reported by -regress- should be useable as-is if
you're
willing to keep in the transformed scale for reporting and
interpretation.
I'd hesitate to advocate back-transforming (exponentiating) the
regression
coefficient and confidence limits:
www.stata.com/statalist/archive/2002-12/msg00193.html . Once you've
made
the commitment to transform the values, it would seem better to stay
with
the transformed scale thereafter.
Both above and below are familiar to recent threads related to the
analysis of proportions. I'm only bringing this up again as I have the
impression most pharmacologists near me overuse ratios. I guess what
bothers me is that using the ratio assumes a particular model, but I do
not think this is appreciated.
Thanks for the comments.
-Dave
Generalized linear modeling with a logarithmic link function would be
another approach, one that could give Wald confidence intervals in the
untransformed metric, e.g., -glm , family(gaussian) link(log) eform-,
but
this would seem to need larger sample sizes than what John has.
Joseph Coveney
-----------------------------------------------------------------------
-----
Nick Cox wrote:
Not my field at all, but the chapter on ratios
in
Rupert G. Miller.
1986 (reissue 1997).
Beyond ANOVA.
New York: John Wiley (London: Chapman and Hall)
looks relevant.
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