I am working on a PK model for data from various tissues. I fit a simple 2CM PK model to the plasma data using 1/Yhat weighting. However, when I build in a compartment (using ASCII model) to model liver concentrations, I don’t know how to keep the 1/Yhat weighting for plasma, but use a different weight (say 1/Y) for the liver data. Is there a way to do this?
The WNL manual mentions a way by defining the weighting variable WT, FUNC 1 F=… WT=1/(F*F) END FUNC 2 F=… WT=1/Y END I never tried myself, will be interested to know if this is working. Jun Shen Seventh Wave Labs
Sorry - a long time in coming to this response but I would suggest this is much easier in the Phoenix models; e.g. here is a snippet of code from a simple PKPD link model where different error models have been applied in the user interface to the conc and effect of multiplicative and additive respectively; 
to give error(EEps = 1) observe(EObs = E + EEps) error(CEps = 1) observe(CObs = C * (1 + CEps)) but yes the different functions you described above should work in WNL classic ascii models Simon
