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Reposted: st: cytel challenge


From   Tero T Kivela <tekivela@cc.helsinki.fi>
To   statalist@hsphsun2.harvard.edu
Subject   Reposted: st: cytel challenge
Date   Mon, 29 Mar 2004 20:07:48 +0300 (EET DST)

On Wed, 21 Nov 2001, Joseph Coveney wrote:

> Lee Sieswerda wrote:
> -------------------------------------beginpost------------------------------
> Cytel makes LogXact for doing "exact" logistic regression (www.cytel.com).
> In their ads they have something called the "Cytel Challenge" where they ask
> people to try to fit a logistic regression model to the following data:
>
> Diar AB Age Hosp
> 0 0 0 0
> 6 0 0 1
> 1.9 0 1 0
> 2.9 0 1 1
> 100 1 1 1
>
> The percentage of patients with diarrhea (Diar) is the outcome and the other
> three variables are predictors: Antibiotic Use (AB; yes/no), Age(young/old),
> Hospital Stay(Hosp;short/long). Taking the challenge using the -logistic- in
> Stata fails to produce a converged model. I really don't know the details of
> how LogXact manages to fit this model, but my question is: would it not be
> possible to program Stata to do "exact" logistic regression and be able to
> fit this model? Or is there something inherently different about Cytel's
> software that it can accomplish this and Stata cannot?
> -----------------------------endpost----------------------------------------
>
> How about:
>
> --------------begin Cytel.do---------------
> insheet using http://www.cytel.com/examples/diarrhea.dat
> generate cou0=totno-diarrhea
> rename diarrhea cou1
> reshape long cou, i(cephalex clindomy sex age los) j(diarrhea)
> glm diarrhea cephalex clindomy sex age los [fweight=cou], irls /*
> */ jknife1 family(binomial) link(logit) eform nolog
> exit
> --------------end Cytel.do----------------------
>
> The estimates for the parameter and its confidence interval for the odds
> ratio for Cephalex are silly, but they're silly in Cytel's solution
> (www.cytel.com/new.pages/LX.ch2a.html), too.  The advertisement claimed to
> be particularly interested in the p-value for the estimate for age.  From
> the looks of Stata's results and those posted on their website, I'd say
> Stata matched their results, and not only for age, but for the estimates for
> the other parameters, as well.
>
> Joseph Coveney
>
> P.S.  Have a look at -permute- and -perm- for a fuller explanation of
> Stata's flexible capabilities in permutation/randomization/exact tests
> custom-made for user-chosen test statistics.
>
>
>
>
>
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