[R] aftreg vs survreg loglogistic aft model (different intercept term)

Immanuel claudio.guerini at unicredit.eu
Thu Nov 25 17:50:05 CET 2010


Hi, I'm estimating a loglogistic aft (accelerated failure time) model, just a
simple plain vanilla one (without time dependent covariates), I'm comparing
the results that I obtain between aftreg (eha package) and survreg(surv
package). If I don't use any covariate the results are identical , if I add
covariates all the coefficients are the same until a precision of 10^4 or
10^-5 except for the intercept term(in survreg)=log(scale) (in aftreg) that
are similar but with a worse precision  of 10^-1 or 10^-2. Any idea of why
this happens? Probably the different covariates coefficients  have a so big
influence on the intercept term?
Thank you

Immanuel
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