Re: st: Configuring Data to percentage ratios

[David Airey <david.airey@vanderbilt.edu>]

> 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.
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/