Different population estimates

From: Toufigh Gordi tgordi@buffalo.edu Subject: [NMusers] Different population estimates Date: 11/17/2003 10:26 AM Dear all, I have run a PK/PD model, estimating all parameters simultaneously. The PK model is a 2-comp with non-linear CL and the PD model is an E-max model. The final run works very well (FOCE) and gives very reasonable parameter estimates. The data is rich (>20/subject) and is from 6 subjects in 6 different dose cohorts (total 36). What I don't really understand is that the population predictions (PRED) are different for within the same dose group. I expected to see identical estimations for subjects receiving the same dose. The estimates are very close to each other, but they are not identical. I am thinking that since PK and PD parameters are estimated at the same time, they do affect each other and thus each subject is its own "population" and hence the differences. Am I correct or is there any other explanation? Thank you, Toufigh Gordi