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st: Re: Cox regression


From   Janet Hill <janethill73@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: Re: Cox regression
Date   Sun, 1 Feb 2009 16:24:58 +0000 (GMT)

I want to use a Cox proportional hazards model with 1
independent variable corresponding to drug types.
There are 3 drugs and for 1 of these there are no
failures.

. xi: stcox i.fadh
i.fadh            _Ifadh_1-3          (naturally
coded; _Ifadh_1 omitted)

         failure _d:  death
   analysis time _t:  dt
Cox regression -- no ties

No. of subjects =           60                    
Number of obs   =        60
No. of failures =           15
Time at risk    =      1326.29
                                                   LR
chi2(2)      =      9.61
Log likelihood  =   -47.766052                    
Prob > chi2     =    0.0082

------------------------------------------------------------------------------
          _t | Haz. Ratio   Std. Err.      z    P>|z| 
   [95% Conf. Interval]
-------------+----------------------------------------------------------------
    _Ifadh_2 |   1.68e+09   8.79e+08    40.49   0.000 
   5.99e+08    4.68e+09
    _Ifadh_3 |   4.33e+09          .        .       . 
          .           .

My question is - how do I handle the situation where
one of the groups has no failures, and how do I
calculate a meaningful hazard ratio.
I have had a look at st_rpool from the Stata FAQ but I
am not convinced that this is a collinearity.
Many thanks.
Janet



      
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