RE: Re: Initial estimates query
From: "Kowalski, Ken" Ken.Kowalski@pfizer.com
Subject: RE: [NMusers] Re: Initial estimates query
Date: Fri, October 17, 2003 7:42 am
Jeff, All,
Yes, whenever I hear one say that a certain set of estimates are realistic
and another set is not, this suggests the modeler has prior information. If
one is in a situation where convergence is overly sensitive to starting
values (a symptom of ill-conditioning) leading to local minima we have
several choices:
1) Collect more data as Bill suggests.
2) Make better use of prior information (e.g., perform a Bayesian analysis,
fix certain estimates based on independent information, etc.)
3) Simplify the model perhaps accepting a less mechanistic one if it meets
the objectives and intended use of the model.
In my opinion, all three strategies above are better than accepting a model
with "realistic" estimates at a known local minimum (i.e., higher OFV than
for another set of feasible but "un-realistic" estimates).
Ken
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