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change calculation of WRES?

From: nele.kaessner
Date: Tue, 25 Aug 2009 14:21:22 +0200

Dear nmusers,

I have a question which I hope is not too trivial for the group. I am
currently analyzing some data where I have more trust in values at late
time points. Therefore, I would like WRES to be a function of time,
putting more weight on late time points. In the help guide I found that
WRES can be influenced by SPTWO, however no real documentation exists (or
I am not aware of it) about how to use it. Does anybody have an example
for me of how to code this?
Moreover, I noticed that no matter how I describe my weighting for IWRES,
this does not at all seem to influence my objective function or parameter
values. When evaluating a model, most people consider anyway that WRES is
what counts, as IWRES are in most cases ok anyway. So my very simple
question is: If this does not influence any of this and I don't use IWRES
to decide if a model is good or bad, why bother at all to calculate them?
I noticed that the standard errors seem to change depending on which
weighting I use for IWRES. Can anybody explain this?

Thanks and best wishes

Dr. Nele Kner
Pharmacometrics -- Modeling and Simulation

Nycomed GmbH
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Received on Tue Aug 25 2009 - 08:21:22 EDT

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