NONMEM Users Network Archive

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RE: Negative concentration from simulation

From: Bill Denney <wdenney>
Date: Tue, 2 Jun 2020 14:30:11 -0400

Hi Nyein,

Negative concentrations can be expected from simulations if the model
includes additive residual error. I assume that you mean additive and
proportional error when you say "combined error model". If the error
structure does not include additive error, then we'd need to know more.

How you will handle them in analysis depends on the goals of the analysis.
Usually, you will either simply set negative values to zero or set all
values below the limit of quantification to zero.

Thanks,

Bill

-----Original Message-----
From: owner-nmusers
Behalf Of Nyein Hsu Maung
Sent: Tuesday, June 2, 2020 2:13 PM
To: nmusers
Subject: [NMusers] Negative concentration from simulation


Dear NONMEM users,
I tried to simulate a new dataset by using a previously published pop pk
model. Their model was described by combined error model for residual
variability. And after simulation, I have obtained two negative
concentrations. I would like to know if there is any proper way to handle
those negative concentrations or if there are some codings to prevent
gaining negative concentrations. Thanks.

Best regards,
Nyein Hsu Maung
Received on Tue Jun 02 2020 - 14:30:11 EDT

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