From:"Venkatesh Atul Bhattaram" 
Subject:[NMusers] FO vs FOCE (Any test?)
Date:Wed, 29 Jan 2003 09:59:51 -0500

Hello All
 
Are there any formal tests to compare the results obtained by FO and FOCE methods?
Could the user group share their experiences in comparing these two methods?
 
Venkatesh Atul Bhattaram
Post-doctoral Fellow
University of Florida
Gainesville-32610
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From:Leonid Gibiansky 
Subject:Re: [NMusers] FO vs FOCE (Any test?)
Date:Wed, 29 Jan 2003 10:35:49 -0500

Hi Atul, 
Here is the summary of my experience: You can plot PRED vs PRED and IPRED vs IPRED to
compare models fitted by FO and FOCE methods. If the points are clustered around the x=y
diagonal then you can use any of the model. If not, prefer FOCE. If you need your model
for simulations, you should care about variances of the random effects and error terms: 
they are more precisely estimated with FOCE. If both the predictions and the variances are similar
between methods, FO can be used. For covariate model development, difference in OF between
the models can be larger for FO. Therefore, after you complete your step-down procedure with
FO, you may test whether additional covariate can be excluded using FOCE fit. With exponential
error model, make sure to use INTERACTION option that does not add time but adds precision. In
general, if you can - then use FOCE; if you cannot (too long runs, does
not converge, etc.), use FO and test the final model with FOCE. 

Good luck, 
Leonid 
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From:"Bachman, William" 
Subject:RE: [NMusers] FO vs FOCE (Any test?)
Date:Wed, 29 Jan 2003 11:02:26 -0500

Some good points here!
 
another aspect: Generally, with sparse data, FO does a reasonably good job.  With dense data, FOCE is recommended.
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From:
Subject:Re: [NMusers] FO vs FOCE (Any test?)
Date:Wed, 29 Jan 2003 11:16:42 -0500

See 

 Assessment of actual significance levels for covariate effects in NONMEM 
 Author                                                      Wahlby U. Jonsson EN. Karlsson MO 
 Journal Title                                               Journal of Pharmacokinetics & Pharmacodynamics 
 Year of Publication                                         2001 
 Volume (Issue)                                              28(3) 
 Pages                                                       231-252

 Commentary on significance levels for covariate effects in NONMEM 
 Author                                                     Beal SL 
 Journal Title                                              Journal of Pharmacokinetics & Pharmacodynamics 
 Year of Publication                                        2002 
 Volume (Issue)                                             29(4) 
 Pages                                                      403-412

Chuanpu 

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Chuanpu Hu, Ph.D.
Research Modeling and Simulation
Clinical Pharmacology Discovery Medicine
GlaxoSmithKline
P.O. Box 13398
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Tel: 919-483-8205  
Fax: 919-483-6380
E-mail: chuanpu.hu@gsk.com
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From:VPIOTROV@PRDBE.jnj.com
Subject:RE: [NMusers] FO vs FOCE (Any test?)
Date:Thu, 30 Jan 2003 15:32:13 +0100

Atul,
 
I don't think you can really test this. Just use FOCE as default if your model and computer resources allow
 
Best regards, 
Vladimir
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