Hi All,
Recently, I am setting up a PKPD model.
In the dataset I have 0 (I put them as blank) for PK concentration and some values for PD for vehicle arm.
I would like to model PKPD simultaneously.
However, what I found is that the PK estimation will be biased by those missing value in concentration.
I try to use the following code to avoid that but without total success.
--
observe(CObs = (Nominal_dose==0?0:C) * (1 + CEps))
--
I will get different parameter estimates and a warning saying:
Warning: Cannot determine error variance - 1.0 assumed
Any suggestion?
Thank you very much,
Shu-Pei