Some basic modeling results

From: "Willavize, Susan A" susan.a.willavize@pfizer.com Subject: [NMusers] Some basic modeling results Date: Thu, 5 Oct 2006 08:26:05 -0400 I will be meeting in about 3 hours time with a fellow student at Univ Buffalo. We will be discussing nonlinear mixed effects modeling of PK/PD data. I am relatively new to this area of study. There are two things that I recall being taught which I wish to discuss with him. 1.) that the FO method tends to provide more biased estimates of population mean parameters than FOCE. And 2.) that if we fit a between subject variance model (Omega) that is too simple (i.e. diagonal when it should be including covariances) then our estimates of the variability of the fixed effects parameters (and predictions of mean responses) are likely to be underestimated. Are these two things true? Can you show me literature references about this? Thank you in advance for helping me with my homework. Susan