# Re: Fwd: T in \$DES

From: Jakob Ribbing <jakob.ribbing>
Date: Tue, 6 Jul 2021 15:15:44 +0200

Dear Matts,

Did you get funny results in the way that using T_DAY did now work as inten=
ded?
If you are unsure you could set up a simple test where you have the analyti=
cal solution to the output, as an initial confirmation.

Otherwise, for models integrating forward in time, a covariate value at tim=
e 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 next reco=
rd 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 fine.
The output in the table at time zero would be the subject’s last va=
lue because it has not yet entered \$DES at time zero, but integrating forwa=
rd that should not impact the fit (I believe).

Best regards

Jakob

> On 6 Jul 2021, at 14:44, Matts Kågedal <mattskagedal
e:
>
> Hi all,
> I have a question regaring T in \$DES.
> I have a time-varying covariate that is derived based on an explicit equa=
tion and then use in a differential equation.
> I got some funny results in the output table and investigated a bit furth=
er.
>
> 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=
e patient? I was expecting it to be Zero (same as Time). Seems to be the sa=
me 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 - 09:15:44 EDT

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