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
[email protected] tel:+64(9)923-6730 fax:+64(9)373-7090
mobile: +33 64 271-6369 (Apr 6-Jul 20 2009)
http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford
