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Re: st: Stata not recommended for exact 2x2 test

From   David Airey <>
Subject   Re: st: Stata not recommended for exact 2x2 test
Date   Mon, 10 Nov 2008 16:14:16 -0600

If anyone needs access to this paper (within reason, so I don't get sued) email me. I sent Joseph a copy.


On Nov 10, 2008, at 9:47 AM, Joseph Coveney wrote:

David Airey  wrote:

I was looking at the following citation, and found the author
explicitly argued against using Stata for a particular 2x2 exact test.

[Quote from article:] (ii) Comparative trials (singly conditioned).
These correspond to the usual experimental design in biomedical work, in which a sample of convenience is randomized into two treatment groups, so that the group (column) totals are fixed in advance. The proper tests of significance are exact tests on the odds ratio, on the ratio of proportions (relative risk and risk ratio) or on the difference between proportions.
[snip]                       . . . for an exact test on OR=1,
it is safe only to use the Testimate single-conditioned
option. For the exact test on RR=1, and for the exact
test on the difference in proportions (p2 - p1=0), it is
safe to use StatXact and Testimate, but not Stata.



Did Prof. Ludbrook (or anybody) indicate what algorithms Testimate 6.0 uses for exact tests of odds ratio = 1, relative risk = 1 and risk difference = 0
in the randomized clincial trial (single-conditioned) situation?

Joseph Coveney

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