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RE: st: _tabi, exact_ gives obviously wrong P-value


From   Richard Williams <[email protected]>
To   [email protected]
Subject   RE: st: _tabi, exact_ gives obviously wrong P-value
Date   Wed, 22 Dec 2004 13:13:14 -0500

At 12:58 PM 12/22/2004 -0500, Steichen, Thomas J. wrote:


What version of tabi and Stata are you running, Marcello?

I get:

.. tabi 27879 35177 29377 17201 \ 118 187 183 65, e chi2

           |                     col
       row |         1          2          3          4 |     Total
-----------+--------------------------------------------+----------
         1 |    27,879     35,177     29,377     17,201 |   109,634
         2 |       118        187        183         65 |       553
-----------+--------------------------------------------+----------
     Total |    27,997     35,364     29,560     17,266 |   110,187

          Pearson chi2(3) =  17.7073   Pr = 0.001
           Fisher's exact =                 1.000
I'm with Thomas on this one. I ran it this morning and got the above results. Then I did an update all (there is a Dec. 20 update for those who haven't noticed) and again got the above results.

HOWEVER -- I ran the problem in Stata 7 -- and got

Pearson chi2(3) = 17.7073 Pr = 0.001
Fisher's exact = 0.001

There has been some fiddling around with the algorithm for Fisher's exact test to make it faster -- has accuracy perhaps been compromised in the process?


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Richard Williams, Notre Dame Dept of Sociology
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