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st: weibull with frailty and ancillary parameters


From   Aysegul Aydin <Aysegul.Aydin@Colorado.EDU>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: weibull with frailty and ancillary parameters
Date   Tue, 14 Aug 2007 20:08:15 -0600

Dear Statalisters,

I have a question about a Stata command that Blossfeld, Golsch and Rohwer
use in their book "Event History Analysis with Stata" (p. 202).

The command is;

streg edu coho2 coho3 lfx pnoj pres, dist(w) time///
ancillary (edu coho2 coho3 lfx pnoj pres) 

where the ancillary option links the covariates to what the authors call b
parameters.

My question is;

1) What purpose do the ancillary parameters serve? It is my understanding
that the ancillary parameters directly estimate the individual effect of a
covariate on duration dependence whereas in standard weibull regression, the
model produces a duration dependence parameter p but does not allow the
researcher to analyze such individual impacts. Is this right? 

2) Is it possible to use this command with the frailty option? Right now,
Stata refuses to allow the frailty option with 'ancillary'. Are you aware of
other ways to integrate frailty into the model? 

Thanks very much in advance and Kind Regards,

Aysegul



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