We are running survival models with a large data base with multiple
observations per case. We have run a variety of models with frailty
(shared and unshared) with no problem. However, when we test our arguments
using an exponential model with frailty, we can't get it to converge, even
when we follow the advice in the stata manual to invoke the "difficult"
option (p. 199, Survival Analysis and Epidemiological Tables). Since this
advice appears to pre-suppose convergence problems with frailty models, we
are wondering if anyone has any advice/suggestions for understanding what
the problem might be in the case of our exponential model. Thanks
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