RE: [NMusers] Visual predictive check!

Ken and All,
 
The recent paper on JPP "Impact on censoring data below an arbitrary =
quantification limit on structural model misspecification" 2008, =
35:101-16, by Byron, Fletcher and Brundage is still fully available on =
line and it speaks volumes about bioanalytical motivated LLOQ and =
pharmacokinetics modeling. Just for those who haven't read it, I vividly =
reccomend so.
Cheers
 
 
---------------------------------------------------------------
Luis M. Pereira, Ph.D.
Assistant Professor, Pharmacometrics
Massachusetts College of Pharmacy and Health Sciences
Childrens Hospital Boston / Harvard Medical School
179 Longwood Ave, Boston, MA 02115
Phone: (617) 732-2905
Fax: (617) 732-2228
 

________________________________

From: owner-nmusers_at_globomaxnm.com on behalf of Ken Kowalski
Sent: Fri 5/23/2008 11:22 AM
To: 'Nick Holford'; nmusers_at_globomaxnm.com
Subject: RE: [NMusers] Visual predictive check!



Nick,

Yes, I'm making the assumption that a measured concentration cannot be
negative. Educate me about chemical assays. Can you get troughs rather
than peaks in a chromatogram such that the area below zero is integrated =
and
reported as a negative concentration? If so, what would happen if you
assayed a bunch of pre-dose samples (before drug is administered) where =
the
true mean concentration is zero? Would we get measured concentrations
symmetrically distributed about zero (with about 50% of the measured
concentrations reported as negative and 50% positive)? If so, then a =
normal
residual error model may indeed be appropriate.

Ken



Received on Sat May 24 2008 - 19:58:23 EDT