NONMEM Users Network Archive

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Re: computation of exponential error model for RUV

From: Jakob Ribbing <jakob.ribbing>
Date: Mon, 19 Jul 2021 18:03:15 +0200

Dear Monia,

Yes, that is correct.
So if one were to use this parameterization for FOCE then one would effecti=
vely get a proportional (symmetric) error distribution, exactly according t=
o what you suggested:
Y=F*(1+EPS(1))

For this reason, the standard approach in NONMEM (for FOCE and exponential =
RUV), is to log-transform both sides, i.e.like this:
 
$ERROR (OBSERVATION ONLY)
 DEL=0.0000001
 IPRED=LOG(F+DEL)
 Y=IPRED+EPS(1)

So additive on the log-transformed scale is exactly the error model you wou=
ld like to use.
Maybe that would be a solution for your comparison?

Best wishes

Jakob




> On 19 Jul 2021, at 17:34, Guidi Monia <Monia.Guidi
>
> Dear colleagues,
>
> We would like to compare the NONMEM predictions with those obtained by a =
Bayesian TDM software for models describing the residual unexplained variab=
ility with exponential errors.
>
> We need to know if NONMEM performs a first order Taylor expansion of the =
exponential error when data are fitted by the FOCE method:
> Y=F*EXP(EPS(1)) -> Y= F*(1+EPS(1)).
>
> Could someone help with this?
> Thanks in advance
> Monia
>
> Monia Guidi, PhD
>
> Pharmacometrician
> Service of Clinical Pharmacology | University Hospital and University of =
Lausanne
> Center of research and innovation in Clinical Pharmaceutical Sciences | U=
niversity Hospital and University of Lausanne
> BU17 01/193
> CH-1011 Lausanne
> email: monia.guidi
> tel: +41 21 314 38 97
>
>
> CHUV
> centre hospitalier universitaire vaudois
>
> <image001.png>


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Received on Mon Jul 19 2021 - 12:03:15 EDT

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