Hi,
Its not clear to me what Mark had in mind when he asked if " mixed
effect modeling (NONMEM in particular) is robust".
But Susan proposes its just obviously OK <grin> and Yaning suggests
reading a book for the simple case of linear models. But what about the
real world i.e. non-linear mixed models?
And surely there must be some degree of imbalance that would lead to a
non-robust description when using a mixed model? e.g. if one is trying
to described a disease progress curve and some people are followed long
enough to identify an exponential shape while others are followed for a
shorter time and appear to have a linear shape then wouldn't there be
some bias in the resulting estimates describing the curve depending on
the mix of short or long follow up times?
Nick
Willavize, Susan wrote:
Hi Mark,
This should be true just based on the nature of mixed effects modeling.
If you are not convinced, you may want to try some examples where you
simulate balanced and unbalanced designs and then estimate. J
Best Regard
Wang, Yaning wrote:
Linear Mixed Models for Longitudinal Data by Geert Verbeke
<http://www.amazon.com/exec/obidos/search-handle-url/102-2006236-4753744?%5Fencoding=UTF8&search-type=ss&index=books&field-author=Geert%20Verbeke>,
Geert Molenberghs
<http://www.amazon.com/exec/obidos/search-handle-url/102-2006236-4753744?%5Fencoding=UTF8&search-type=ss&index=books&field-author=Geert%20Molenberghs>
Yaning Wang, Ph.D.
Team Leader, Pharmacometrics
Office of Clinical Pharmacology
Office of Translational Science
Center for Drug Evaluation and Research
U.S. Food and Drug Administration
Phone: 301-796-1624
Email: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
"The contents of this message are mine personally and do not
necessarily reflect any position of the Government or the Food and
Drug Administration."
------------------------------------------------------------------------
*From:* [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] *On Behalf Of *Mark Sale - Next
Level Solutions
*Sent:* Tuesday, September 02, 2008 1:28 PM
*To:* nmusers@globomaxnm.com
*Subject:* [NMusers] unbalanced design
Does anyone have a reference to a publication assessing whetheor
unbalances studies? I see if in a number of courses (including the
original beginners course for NONMEM), but can't find a publication.
thanks
Mark Sale MD
Next Level Solutions, LLC
www.NextLevelSolns.com <http://www.NextLevelSolns.com>
919-846-9185
--
Nick Holford, Dept Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand
[EMAIL PROTECTED] tel:+64(9)923-6730 fax:+64(9)373-7090
http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford
