no. of dummy points affect simulation and estimation results

From: Sandra.Visser@astrazeneca.com Subject: [NMusers] no. of dummy points affect simulation and estimation results Date: Mon., April 20, 2004 09:10 Dear Nonmem users, I try to fit a set of 5 differential equations in the ADVAN6 or ADVAN9 subroutine to a dataset with observations every 20 min for two days. I initialize each PD compartment via AMT=X with MDV=1 for each compartment at time 0. It appeared that the time to steady state in the set of equations is appr. 2 days. Therefore, I have added dummy time points (DV=0, MDV=1) for >2 days in order in order to allow sufficient time to steady state. However, it appears to be that both simulation and estimation results depend on the number and the particular placement of the dummy time points. Adding dummy time points each 20 min for several days seems to give the resonable results but calculation time rises substantially, which I would like to avoid. Does anyone know how to select the optimum number and times of the dummy points? And could anyone give me some information on the integration routines that are used in the ADVAN6, 8 and 9 subroutines and the selection of the stepsize. I would appreciate any ideas or suggestions on this matter. Best regards, Sandra Visser