Re: Reducing ETAs actually decreased OFV
Hi Xinting,
When I've seen this before, it is due to the model approaching non-convergence.
Given the model that you're showing below, I'd guess that your issue is coming
from the eta on Q or V3 because it is rare to have enough data to fit true IIV
there.
Thanks,
Bill
Quoted reply history
On Aug 25, 2013, at 8:42, "Xinting Wang"
<[email protected]<mailto:[email protected]>> wrote:
Dear Leonid,
I tried with your method and found the same result. The initial estimation of
the added ETA was set at 0.01, and the result showed an increase of OFV. Please
see below the $PK part of the control file for more information. Many thanks.
Dear Bill,
Could you please explain that in a little bit more detail? I am pasting the $PK
part of the control file in case you could find the useful information. Thanks
a lot.
$PK
FA1=0
FA2=0
FA3=0
FA4=0
IF(DOSE.EQ.250) THEN
FA1=1
ENDIF
IF(DOSE.EQ.500) THEN
FA2=1
ENDIF
IF(DOSE.EQ.850) THEN
FA3=1
ENDIF
IF(DOSE.EQ.1000) THEN
FA4=1
ENDIF
F1=FA1+FA2*THETA(6)+FA3*THETA(7)+FA4*THETA(8)
TVCL=THETA(1)
TVV2=THETA(2)
TVKA=THETA(3)
TVQ=THETA(4)
TVV3=THETA(5)
CL=TVCL*EXP(ETA(1))
V2=TVV2*EXP(ETA(2))
KA=TVKA*EXP(ETA(5))
Q=TVQ*EXP(ETA(3))
V3=TVV3*EXP(ETA(4))
S2=V2/1000
S3=V3/1000
$ERROR
IPRE=F
IRES=DV-IPRE
W=F
IF(W.EQ.0) W = 1
IWRE = IRES/W
Y=F*(1+EPS(1))+EPS(2)
Best Regards
On 12 August 2013 20:50, Denney, William S.
<[email protected]<mailto:[email protected]>> wrote:
Hi Xinting,
In a few rare cases, I've seen this happen if the model is approaching
nonconvergence. In those cases, typically the RSE on one or more parameters
will increase and the ratio of max to min eigenvalues will increase
substantially. Are you seeing either of these?
Thanks,
Bill
On Aug 11, 2013, at 21:56, "Leonid Gibiansky"
<[email protected]<mailto:[email protected]>> wrote:
Xinting,
Try to start from the initial conditions of your "reduced" model but add that
"reduced" ETA with the corresponding OMEGA equal to 0.01 or other small number.
If the control stream code is correct, the objective function should decrease
or retain the same value.
Leonid
--------------------------------------
Leonid Gibiansky, Ph.D.
President, QuantPharm LLC
web: http://www.quantpharm.com
e-mail: LGibiansky at http://quantpharm.com
tel: (301) 767 5566<tel:%28301%29%20767%205566>
On 8/10/2013 10:23 PM, Xinting Wang wrote:
> Dear all,
>
> Does anyone witnessed such a phenomenon in NONMEM as when you reduced an
> ETA, the OFV value, rather than increase, actually decreased? It's quite
> against intuition, as individual estimation should be better than
> population estimation in that particular parameter. Both models, whether
> having this ETA, converged very well.
>
> Best
>
> --
> Xinting
--
Xinting