Re: [NMusers] Visual predictive check!

Luis,

A very good suggestion. I agree this is an excellent piece of work
dealing with the LLOQ problem. It provides a clear example of the
benefits of the YLO option in NONMEM for dealing with censored data.

By the way the first author is Wonkyung BYON -- not Byron.

Best wishes,

Nick

Luis.Pereira_at_mcphs.edu wrote:
> 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
>

--
Nick Holford, Dept Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand
n.holford_at_auckland.ac.nz tel:+64(9)373-7599x86730 fax:+64(9)373-7090
www.health.auckland.ac.nz/pharmacology/staff/nholford


Received on Sun May 25 2008 - 02:12:55 EDT