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From |
Janet Hill <janethill73@yahoo.co.uk> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Re: Cox regression |

Date |
Mon, 2 Feb 2009 09:59:09 +0000 (GMT) |

Steve, Thanks for that, I thought that might be the case. I will look into exact tests. I think that the distribution of the censoring times will preclude the use of Fisher. Janet --- Steven Samuels <sjhsamuels@earthlink.net> wrote: > Janet, You cannot fit a hazard model to a group with > no observed > failures. However your main problem is that you > have too few > failures to trust the Cox results. The p-values > from the Cox mode > require larger sample sizes. Plot the survival > curves with the > asymptotic CI's (-sts graph-) and see how wide they > are. Your only > recourse is to an "exact" test. At least one such > exact long-rank > test has been published, but I don't have the > reference offhand. If > follow-up times are similar among the censored > observations, or the > distributions of censoring times in the three groups > are similar, you > can try pairwise Fisher's exact tests with failure > as a binary outcome. > > Steve > > > 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. > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**Re: st: Re: Cox regression***From:*Steven Samuels <sjhsamuels@earthlink.net>

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