Inclusion of covariates and model improvement

From: "Gordi, Toufigh" Toufigh.Gordi@cvt.com Subject: [NMusers] Inclusion of covariates and model improvement Date: Wed, 19 Oct 2005 15:12:06 -0700 Dear all, I have applied a 3-comp PK model with IIV on CL and VC on some data (FOCE INTERACTION). Graphical inspections indicated a weak correlation between VC and body weight. When BW was incorporated in the model, affecting VC, the OFV dropped by over 20 points. VC is described as: VC=THETA(x)*BW THETA(x) is estimated to be 0.15. There are not much differences in model parameters between the simple and the more complex model, incorporating the BW. However, parameter CVs are mostly worse for the latter, and the IIV corresponding to VC is only slightly decreased (from 0.35 to 0.26), while its CV has increased from 26% in the simple model to 59% in the complex model. I am reluctant to present the more complex model as the final one despite the significant decrease in OFV. Any comments on which model is preferred? Toufigh Gordi