RE: OFV from different algorithms

It seems there have been two different questions posed on the same subject line. I will deal with each one separately. 1) The original question from Mark Tepeck has been answered by Leonid Gibiansky, that generally when covariate model comparisons are performed, the OFV from the same estimation algorithm should be used (Imp with IMP, FOCEI with FOCEI, etc.) 2) The question about how the absorption-two compartment model modeled in ADVAN6 (or the other ODE ADVANs) compares to the in-line analytical ADVAN4 version, can be answered as follows: If the models built using ADVAN4 and ADVAN6 are identical in every way with respect to the user's setup (residual variance, OMEGA layout lag times, bioavailability, etc.), then the OFV between these two should be very close, within less than one OFV. The difference between finite difference evaluation of derivatives versus analytical derivatives, should not cause a difference of more than that. There may be exceptions to this if a model is quite complex with potential numerical issues. Dennis's particular experience of a difference of 60 units suggests that the models were not set up identically in ADVN4 versus ADVAN6. I believe Luann Philipps in her response was addressing this possibility. By the way, many modelers favor ADVAN13 as the go-to ODE solver. Robert J. Bauer, Ph.D. Senior Director Pharmacometrics R&D ICON Early Phase 820 W. Diamond Avenue Suite 100 Gaithersburg, MD 20878 Office: (215) 616-6428 Mobile: (925) 286-0769 [email protected] www.iconplc.com