Error model

From: Jenny <zheng.22@osu.edu> Subject: Error model Date: Thu, 21 Jan 1999 11:53:50 -0800 Dear NONMEM users, I am trying to build a Statistical Model. When I used additive model, the residual plot wres vs. pred is V-shaped, i.e., wider wres at high pred. When I used CCV error model, the plot is a reversed V-shape, i.e., wider wres at low pred. Therefore, I tried the power function model. The objective function did decreased, but the residual plot show a linear relationship, where the wres is more negative at high pred, wres is more positive at low pred. So far, I haven't got a good error model. If anyone has any suggestions, you are highly appreciated.