Model building

Hi, I am in the process of developing a PK/PD model and have a naive question regarding model building. I currently do not have all the PD data and more data would be available in the future. For the current data set, I have tried models say A to D. Now model A (cell kill) and B (cell kill +transduction) converges using FOCE (no CV% but I am willing to live with that) but from the RES and WRES plots we can clearly see that there is some bias. The fit is OK but not great. The ofv values are around 400. Now models B (cell cycle specific kill), C (cell + precursor cell kill +transduction) and D (cell cycle specific + indirect response model) do not converge using FO or FOCE methods but when I look at the fits from the terminated runs, the fits are much better than those obtained with Model A, and there seems very little bias. Also the ofv values are between 160-250. So my question is whether the fits, RES, WRES plots and the ofv values have meaning even when the minimization terminates. Regards Neil -- Indranil Bhattacharya