NONMEM Users Network Archive

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RE: OFV from different algorithms

From: Luann Phillips <Luann.Phillips>
Date: Thu, 24 Sep 2020 01:04:14 +0000

Dennis,

I would be curious if you get the same difference in OF value if you do the=
 following for the ADVAN6 version:

Same initial estimates between the 2 ADVANs

$ESTIMATION use the options SORT, SIGDIG=3, SIGL=9

$SUBROUTINE ADVAN6 TOL=9

If $ERROR is %CV or Log error model, include
DFLAG=0
IF(CMT.EQ.DOSING CMT) DFLAG=1
For the %CV set IPRED=F+DFLAG
For Log error set IPRED=LOG(F+DFLAG)
This helps handle the first oral dose record more consistently between adva=
n4 and advan6

Over the years, I've seen differences for the same model between 2 advans b=
ecome more similar.

Luann Phillips
Distinguished Scientist, Pharmacometrics
Cognigen Corporation, a Simulations Plus company

From: owner-nmusers
 Of Dennis Fisher
Sent: Wednesday, September 23, 2020 8:36 PM
To: Mark Tepeck <mark.tepeck
Cc: nmusers
Subject: Re: [NMusers] OFV from different algorithms

Mark

I posed a variant of this question to Stu Beal (Sheiner's statistician) > 2=
0 years ago. He answered that one cannot compare ADVAN's, e.g., between AD=
VAN4 and ADVAN6 for the identical model.
I verified this today when I ran a model with those two ADVAN's -- both con=
verged, they yielded quite similar parameter estimates, but the OF differed=
 by 60 units.

I will be interested to hear Bob Bauer's reply to this issue.

Dennis

Dennis Fisher MD
P < (The "P Less Than" Company)
Phone / Fax: 1-866-PLessThan (1-866-753-7784)
www.PLessThan.com<http://www.plessthan.com/>




On Sep 23, 2020, at 5:09 PM, Mark Tepeck <mark.tepeck
.tepeck

Hi NMusers,

I believe below is a very common question, but I could not find a
clear answer in literature.

Sometimes, we want to find out which algorithm offers the better model
fitting for a given dataset.

Is it possible to use the objective function value (OFV) to compare
the model fitting computed by various algorithms (e.g. FOCE, IMP, and
SAEM) ? Put it into another way, the same input dataset with the same
fitted model/estimates will lead to similar OFVs among FOCE, IMP, and
SAEM?


Thanks,


Mark


Received on Wed Sep 23 2020 - 21:04:14 EDT

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