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st: Other definition of -tabodds-?


From   "Herve STOLOWY" <stolowy@hec.fr>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Other definition of -tabodds-?
Date   Wed, 13 Aug 2008 18:21:05 +0200

Dear Statalisters:

I use -tabodds- to compute two ratios (cases/controls) (20/13 and  22/11 in the example below) and test the evolution of these ratios (see the output below).

tabodds small_profit post_ifrs if country=="AUS" & sample_sum==1

--------------------------------------------------------------------------
 post_ifrs  |      cases     controls       odds      [95% Conf. Interval]
------------+-------------------------------------------------------------
          0 |         20           13    1.53846        0.76531   3.09270
          1 |         22           11    2.00000        0.96985   4.12436
--------------------------------------------------------------------------
Test of homogeneity (equal odds): chi2(1)  =     0.26
                                  Pr>chi2  =   0.6115

Score test for trend of odds:     chi2(1)  =     0.26
                                  Pr>chi2  =   0.6115

I would like to define the ratios in a different way:

Instead of cases/controls, I would like to have:

(cases-controls)/(cases+controls).

With the -matrix- command and scalars, I manage to get the ratios:

count if post_ifrs==0 & small_profit==1 &  country=="AUS" & sample_sum==1
scalar N1 = r(N)
count if post_ifrs==0 & small_profit==0 &  country=="AUS" & sample_sum==1
scalar N2 = r(N)
scalar odds=(N1-N2)/(N1+N2)
matrix m1 = N1, N2, odds
matrix rownames m1 = "Pre IFRS"
count if post_ifrs==1 & small_profit==1 &  country=="AUS" & sample_sum==1
scalar N3 = r(N)
count if post_ifrs==1 & small_profit==0 &  country=="AUS" & sample_sum==1
scalar N4 = r(N)
scalar odds2=(N3-N4)/(N3+N4)
matrix m2 = N3, N4, odds2
matrix rownames m2 = "Post IFRS"
matrix m3 = m1\m2
matrix colnames m3 = "Cases (Small profit)" "Controls (Small loss)" Odds
matrix list m3

Here is the output:

m3[2,3]
            Cases (Small profit)  Controls (Small loss)                   Odds
 Pre IFRS                     20                     13              .21212121
Post IFRS                     22                     11              .33333333


I would like to know if there is an equivalent command to -tabodds- or a specific way to test the evolution of the two ratios:


(N1-N2)/(N1+N2) 
(N3-N4)/(N3+N4)

respectively 0.2121 and 0.3333 in my example.

Best regards

Herve Stolowy











***********************************************************
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HEC Paris
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Tel: +33 1 39 67 94 42 - Fax: +33 1 39 67 70 86
mail: stolowy at hec dot fr
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