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st: dealing with 0 in cells in 2x2 tables


From   "Beynon, Caryl" <C.M.Beynon@ljmu.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: dealing with 0 in cells in 2x2 tables
Date   Fri, 27 Jun 2008 15:02:03 +0100

Hello All, my first post so be honest if you feel this type of question
is not suitable for this forum - any help gratefully received. 

I am building a logistic regression model but first I wish to carry out
bivarite analyses measuring the effect of each exposure on the outcome.
In my 2 by 2 table I have 0 in one cell so the odds ratio is either
infinity of 0. However, the chi square test shows that the exposure
(homelessness) is significantly associated with the outcome, so I cannot
simply ignore this variable in my bivarite and multivariate analyses.
How do people deal with this situation? 

Thanks,
Caryl 

tabodds  spoonB_vis_writ   homeless2

------------------------------------------------------------------------
--
 homeless2  |      cases     controls       odds      [95% Conf.
Interval]
------------+-----------------------------------------------------------
--
         No |          0           22    0.00000              .
.
        Yes |         22          119    0.18487        0.11731
0.29135
------------------------------------------------------------------------
--
Test of homogeneity (equal odds): chi2(1)  =     3.94
                                  Pr>chi2  =   0.0470

Score test for trend of odds:     chi2(1)  =     3.94
                                  Pr>chi2  =   0.0470

. mhodds  spoonB_vis_writ   homeless2

Maximum likelihood estimate of the odds ratio
Comparing homeless2==1 vs. homeless2==0

    ----------------------------------------------------------------
     Odds Ratio    chi2(1)        P>chi2        [95% Conf. Interval]
    ----------------------------------------------------------------
              .       3.94        0.0470                .          .
    ----------------------------------------------------------------

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