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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