RE: OMEGA BLOCK with mixture model?

Mats > With oral data only I would normally model with BLOCK(2) on > CL/F and V/F or a DIAG(3) on CL/F, V/F and relative F. The > latter may have some advantages for diagnostics, covariate > model building etc. I have often seen these two options considered. I am unclear as to the advantages of DIAG(3) over BLOCK(2)? In theory it would seem that they should be identical. In practice it seems that DIAG(3) is more relaxed since it is not required that the variance of relative F if reassigned to the covariance of (CL/F, V/F) [under BLOCK(2)] yields a positive definite matrix. I presume an advantage wrt covariate model building would be access to the EBEs of F_i. However, given the variance of F_i may exceed the covariance of (CL/F, V/F) then I wonder if this is a real advantage or an artefact of numerical procedures? I am keen to learn more about real advantages of application of DIAG(3) as an alternative to BLOCK(2). Steve -- Professor Stephen Duffull Chair of Clinical Pharmacy School of Pharmacy University of Otago PO Box 913 Dunedin New Zealand E: [email protected] P: +64 3 479 5044 F: +64 3 479 7034 Design software: www.winpopt.com