One can get PRED at BQLs using COMACT option, see manual:
"COMACT=1 is a pass with final thetas and zero-valued etas".
Things computed at this stage are based on THETAS with zero ETAs and
thus provide PRED values. E.g.,
IPRED = ...
IF(COMACT==1) PRED1=IPRED
creates the PRED1 variable that is a population prediction even at BQL
records.
Have not tried it but it looks like it can be used to create population
predictions of other derived variables as well (like AUC, half-life,
etc.) that need to be computed based on THETAs (with ETAs equal to zero).
Leonid
On 2/22/2019 5:11 AM, Smit, Cornelis (Klinische Farmacie) wrote:
Hi Andrew,
When your observation is <BLQ, M3 gives you a likelihood of this value
being < BLQ in the PRED column. So this value will be close to 1 when
the model is fairly sure that the concentration should be BLQ. This
might explain why the PREDs might be relatively high in your diagnostics
here. I usually exlude the <BLQ values in my GOF diagnostics, and check
for model misspecification with a VPC showing BLQ data (as described in
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2691472/ ). You can do this
with the old xpose package. I don’t think there is any way to visualize
the BLQ prediction in the ‘usual’ GOF but I’m very curious if someone
else has some ideas regarding this.
Kind regards,
*Cornelis Smit*
Hospital Pharmacist / PhD candidate
Dept. of Clinical Pharmacy
St. Antonius Hospital
Dept. of Pharmacology,
Leiden Academic Centre for Drug Research,
Leiden University, Leiden, The Netherlands
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*Van:*[email protected] [mailto:[email protected]]
*Namens *Andrew Tse
*Verzonden:* vrijdag 22 februari 2019 10:23
*Aan:* [email protected]
*Onderwerp:* [NMusers] Strange PRED prediction in SAEM with M3 BQL handling
Dear all,
I am running SAEM with M3 BQL handling method via PsN but having some
strange PRED values in mytab table if someone can shed some light:
I have tried using FOCE (excluding BQL data) & SAEM (excluding BQL data)
both have normal looking fitting with data in individual plots.
Once I have coded SAEM with M3 codes and include BQL data it showed very
strange PRED vs time plots (eg. 100 times over prediction at BQL time
point). IPRED had normal results.
Here are the control stream that I have used:
$PK
TVCL=THETA(1)
MU_1=LOG(TVCL)
CL=EXP(MU_1+ETA(1))
TVV2=THETA(2)
MU_2=LOG(TVV2)
V2=EXP(MU_2+ETA(2))
TVQ=THETA(3)
MU_3=LOG(TVQ)
Q=EXP(MU_3+ETA(3))
TVV3=THETA(4)
MU_4=LOG(TVV3)
V3=EXP(MU_4+ETA(4))
K23=Q/V2 ;Distribution rate constant
K32=Q/V3 ;Distribution rate constant
KA=0
A_0(1)=0
A_0(2)=0
A_0(3)=0
$DES
DADT(1)= -KA*A(1)
DADT(2)= -CL*A(2)/V2-K23*A(2)+K32*A(3)
DADT(3)= K23*A(2)-K32*A(3)
$ERROR
IPRED=A(2)/V2
W=SQRT(THETA(5)**2+((THETA(6)*IPRED)**2))
IF (LIMI.EQ.1) LIM= 0.05 ;BATCH 1
IF (LIMI.EQ.2) LIM= 0.01 ;BATCH 2
IF (LIMI.EQ.3) LIM= 0.025 ;BATCH 3
IF(BQL.EQ.0) THEN
F_FLAG=0
Y=IPRED+W*ERR(1)
ELSE
F_FLAG=1 ;BQL so Y is likelihood
Y=PHI((LIM-IPRED)/W)
ENDIF
IWRES=(DV-IPRED)/W
IRES=DV-IPRED
My question is that whether there is error in my M3 $ERROR model? or
whether PRED values for BQL means something else other than prediction
for BQL data?
Thanks a lot.
Kind regards,
Andrew Tse
Research Pharmacist
