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st: frailty models

From   Farzaneh Amanpour <>
Subject   st: frailty models
Date   Sat, 30 Jul 2011 01:56:35 -0700

Dear all,
I have fitted gamma model to the survival data, and maximum likelihood
converged to the solution and I could get the result. But when I added
frailty component (gamma or inverse-Gaussian) to the model, I got this
“Could not calculate numerical derivatives – missing values encountered”
My dataset doesn’t have any missing values, and also when I fit other
distributions like lognormal with frailty component, I don’t encounter
this error.
I would  be grateful if anyone can help me with this problem.
Thank you in advance,

Farzaneh Amanpour

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