From: Stephen Duffull <*stephen.duffull*>

Date: Thu, 16 Apr 2009 20:13:00 +1200

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 adv=

antages 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 covari=

ance 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: stephen.duffull

P: +64 3 479 5044

F: +64 3 479 7034

Design software: www.winpopt.com

Received on Thu Apr 16 2009 - 04:13:00 EDT

Date: Thu, 16 Apr 2009 20:13:00 +1200

Mats

I have often seen these two options considered. I am unclear as to the adv=

antages 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 covari=

ance 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: stephen.duffull

P: +64 3 479 5044

F: +64 3 479 7034

Design software: www.winpopt.com

Received on Thu Apr 16 2009 - 04:13:00 EDT