NONMEM Users Network Archive

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Re: OMEGA off-diagonal elements parameterized as correlations

From: Nick Holford <n.holford>
Date: Wed, 08 Jul 2009 17:07:00 +0200

Paolo,

I too was disappointed when NONMEM VI appeared without the $OMEGA
CORRELATION option. I agree with you that correlations are more
intuitive and easier to use than covariances.

Unfortunately NONMEM VII beta continues with the same lack of support
for a CORRELATION option.

 AN ERROR WAS FOUND IN THE CONTROL STATEMENTS.

 AN ERROR WAS FOUND ON LINE 12 AT THE APPROXIMATE POSITION NOTED:
 $OMEGA BLOCK(3) CORRELATION
                           X
 584 THIS FEATURE IS NOT PART OF NONMEM VII.

I wonder if someone from the NONMEM development team could explain why
this feature remains unimplemented?

Nick

Paolo Denti wrote:
> Dear all,
> I was wondering if it is possible to insert the off-diagonal elements
> of OMEGA as correlations rather than covariances, because I find it
> more intuitive.
>
> To my greatest happiness, I found the following information in a
> NONMEM chm help file:
>
> ___________________________________________________________________
> | |
> | $OMEGA |
> |_________________________________________________________________|
>
> MEANING: Supplies initial estimates for the NONMEM OMEGA Matrix
> CONTEXT: NM-TRAN Control Record
>
> USAGE:
> $OMEGA [DIAGONAL(n)|BLOCK(n)|BLOCK(n) SAME|BLOCK SAME] 5
> [[value1] [value2] [value3] ... [FIXED]] 5
> $OMEGA [DIAGONAL(n)|BLOCK(n)|BLOCK(n,m) L
> [[value1] [value2] [value3]] ... L
> [VARIANCE|STANDARD] [COVARIANCE|CORRELATON] L
> [FIXED] [ALLOFFFIX] [FIRSTFIXED] [PRINCIPAL]] L
> |BLOCK(n) SAME|BLOCK SAME] L
>
> SAMPLE:
> $OMEGA BLOCK(3) 6. .005 .3 .0002 .006 .4
>
> Reading on in the file, the [COVARIANCE|CORRELATON] sounded (in spite
> of the incorrect spelling) like the panacea I was looking for.
> Unfortunately, when I try to compile, I get a message saying that this
> option is not available in NONMEM VI. :-(
> Is this sadly only a feature planned for future versions of NONMEM?
> And if so, does anyone you know of other simple workarounds to use
> correlations instead of covariances?
>
> Thank you in advance,
> Paolo
>
>

--
Nick Holford, Professor Clinical Pharmacology
Dept Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand
n.holford
mobile: +33 64 271-6369 (Apr 6-Jul 20 2009)
http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford

Received on Wed Jul 08 2009 - 11:07:00 EDT

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