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Re: Fwd: T in $DES

From: Matts Kågedal <mattskagedal>
Date: Tue, 6 Jul 2021 16:48:16 +0200

Thanks Jakob and Dennis for helpful comments!
I think the model is doing what it should. My problem is that I don't get
an accurate output of the covariate prediction at time zero when computed
inside $DES based on T_DAY (where T_DAY=T).
As a workaround I now also derive the predicted covariate value in $PK
based on TIME (from the dataset) just for output in $TABLE. This seems to
be working.


On Tue, Jul 6, 2021 at 3:15 PM Jakob Ribbing <jakob.ribbing

> Dear Matts,
> Did you get funny results in the way that using T_DAY did now work as
> intended?
> If you are unsure you could set up a simple test where you have the
> analytical solution to the output, as an initial confirmation.
> Otherwise, for models integrating forward in time, a covariate value at
> time zero (or subjects first time point) would not have an impact on the
> model fit or parameter value, as nonmem would look forward towards the ne=
> record in time.
> $DES isspecial since the solver may move back and forth and time is
> updated in-between data records, but what you try to do may still work fi=
> The output in the table at time zero would be the subject’s last =
> because it has not yet entered $DES at time zero, but integrating forward
> that should not impact the fit (I believe).
> Best regards
> Jakob
> On 6 Jul 2021, at 14:44, Matts Kågedal <mattskagedal
> Hi all,
> I have a question regaring T in $DES.
> I have a time-varying covariate that is derived based on an explicit
> equation and then use in a differential equation.
> I got some funny results in the output table and investigated a bit
> further.
> I therefore derived T_DAY=T in $DES as below and output it in $TABLE.
> Why is T_DAY at TIME=0 equal to the time of the last observation for th=
> patient? I was expecting it to be Zero (same as Time). Seems to be the sa=
> for all IDs in the dataset.
> Below is the output created in $TABLE including the "derived" variable
> T_DAY.
> Any advice would be appreciated.
> Matts Kågedal
> <image.png>
> <image.png>
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Received on Tue Jul 06 2021 - 10:48:16 EDT

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