If you are a WNL user that has recently started to use Phoenix Models (naive pool engine) you might be interested in 'translating' the model weights in WNL to Residual error models in Phoenix models.
To accomplish this here is the correspondance written in PML code.
WNL weight 1/Ypred translates to observe(CObs = C+((C^0.5)*CEps))
WNL weight 1/(Ypred*Ypred) translates to observe(CObs = C+(C*CEps)) or observe (Cobs= C (1+CEPS) which corresponds to the option of residual error model multiplicative.
WNL weight 1/Y translates to observe(CObs = C+((Y^0.5)*CEps)) where Y is the CObs
WNL weight 1/(Y*Y) translates to observe(CObs = C+(Y*CEps)) where Y is the Cobs
In a Phoenix Model Structure tab, you can select the residual error of "custom" and then enter the right hand side of the equations above. For weights that are observed instead of predicted it gets a bit tricky because Phoenix models do not accept CObs in the right hand side of the equations above. To circumvent this one needs to define the concentration as a covariate. Go to the Model Text Tab and write an Exta Column Definition Text, for example
covr(Y<-"conc")
And click refresh
Now the program understands that variable Y (see equations above) correspond to the column 'conc'. Attached is a phoenix project illustrating the 1/y weight and comparing results. This project was created with PHX WNL 6.2. [file name=WNLClassical_WTG.phxproj size=962209]http://www.pharsight.com/extranet/media/kunena/attachments/legacy/files/WNLClassical_WTG.phxproj[/file]
Attached Files
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WNLClassical_WTG.phxproj 939.66KB
378 downloads
Edited by Simon Davis, 20 December 2017 - 04:29 PM.
