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st: Interpreting Theta with gompertzhet


From   "Siyam,AA (pgr)" <A.A.Siyam@lse.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Interpreting Theta with gompertzhet
Date   Mon, 7 Oct 2002 16:41:31 +0100

Dear Stata-listers,

A colleague of mine is asking about how to best interpret the "theta" value following the estimation of a "gompertzhet" model.

As an example, we have the following model:

 xi:gompertzhet time i.sex i.tenureg i.newcohort  i.marstat i.nmm i.socg i.educ i.bathg i.carg i.urind i.pob, dead(outcome) frailty(gamma) robust hr

log relative-hazard form                          Number of obs   =     156134
                                                  Wald chi2(25)   =   29045.86
Log likelihood = -173574.21                       Prob > chi2     =     0.0000
------------------------------------------------------------------------------
             |               Robust
        time | Haz. Ratio   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
     _Isex_1 |   1.850406   .0142284    80.03   0.000     1.822728    1.878504
 _Itenureg_2 |   1.149377   .0092286    17.34   0.000     1.131431    1.167608
 _Itenureg_3 |   1.072943   .0094593     7.99   0.000     1.054563    1.091644
 _Itenureg_4 |   1.642678    .037731    21.61   0.000     1.570366    1.718319
_Inewcohor~2 |   1.709805   .0201656    45.48   0.000     1.670735     1.74979
_Inewcohor~3 |   2.795179   .0342787    83.82   0.000     2.728795    2.863178
_Inewcohor~4 |   4.539291   .0613598   111.91   0.000     4.420607    4.661161
_Inewcohor~5 |   6.999815    .109719   124.14   0.000      6.78804    7.218198
_Inewcohor~6 |   13.94991   .2479541   148.27   0.000      13.4723    14.44445
 _Imarstat_2 |   .9453604    .010464    -5.08   0.000     .9250723    .9660935
 _Imarstat_3 |   1.014716   .0123169     1.20   0.229       .99086    1.039146
 _Imarstat_4 |   1.020194   .0325235     0.63   0.531     .9583996    1.085972
     _Inmm_2 |   1.152044    .016659     9.79   0.000     1.119851    1.185162
     _Inmm_3 |   1.284557    .015833    20.32   0.000     1.253896    1.315966
    _Isocg_2 |   .9955737   .0124997    -0.35   0.724     .9713737    1.020377
    _Isocg_3 |   .9578298   .0123819    -3.33   0.001     .9338665    .9824079
    _Isocg_4 |   .9479021   .0125159    -4.05   0.000     .9236861     .972753
    _Ieduc_1 |   1.040396   .0106443     3.87   0.000     1.019741    1.061469
    _Ieduc_3 |   .9576366   .0229827    -1.80   0.071     .9136344    1.003758
    _Ieduc_4 |   .8596743   .0151121    -8.60   0.000     .8305596    .8898097
   _Ibathg_2 |   1.139885   .0127556    11.70   0.000     1.115157    1.165162
    _Icarg_0 |   1.121058    .008487    15.09   0.000     1.104547    1.137817
    _Icarg_2 |     .94181   .0123203    -4.58   0.000     .9179696    .9662695
   _Iurind_2 |   .9648657   .0075113    -4.59   0.000     .9502555    .9797004
     _Ipob_2 |   .9581827   .0144905    -2.82   0.005     .9301987    .9870086
-------------+----------------------------------------------------------------
       gamma |   .0080562   .0000682   118.09   0.000     .0079225    .0081899
     /ln_the |  -1.996373   .0600449   -33.25   0.000    -2.114059   -1.878687
-------------+----------------------------------------------------------------
       theta |    .135827   .0081557                      .1207469    .1527906
------------------------------------------------------------------------------

We found a great deal of help in understanding the gompertz model from the book "Introduction to Survival Analysis Using Stata" by Cleves,Gould and Gutierrez. But, there seems to be very little explanation of how to use and interpret the "theta" coefficient estimated by the model.


Many thanks for your help in advance.

Best wishes,

Amani

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