RE: categorical covariate with 5 levels
Hi Hong,
Other approaches I can think of are:
1.to plot the EBE of CL vs. different GVHD categories to determine
whether you need a different parameter for each level or indeed you can
(and how to) combine several groups together;
2.since your GVHD variable is an ordinal categorical variable instead of
nominal groups like male and female, you may be able to introduce some
functional form (i.e. treating the covariate as continuous)
Assigning each category with a different parameter is a very intuitive
approach, but the underlying assumption is that each group is different
and no clear pattern exist for the relationship between CL and GVHD.
This might be over-parameterized.
Hope this helps,
Yaming
Quoted reply history
-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Sam Liao
Sent: Friday, July 09, 2010 1:01 AM
To: [email protected]; [email protected]
Subject: RE: [NMusers] categorical covariate with 5 levels
I have a four levels covariate model. Hope this is useful to you.
Sam Liao
Pharmax Research
==========================================================
RA1=0
RA2=0
RA3=0
IF(RACE.EQ.7) RA1=1
IF(RACE.EQ.8) RA2=1
IF(RACE.GT.8) RA3=1
TVCL= TVCL *(1 + THETA(33)*RA1+ THETA(34)*RA2+ THETA(35)*RA3)
-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Hong Li
Sent: Thursday, July 08, 2010 9:01 PM
To: [email protected]
Subject: [NMusers] categorical covariate with 5 levels
Dear all,
I want to build a covariate model for the pk of a drug which is
metabolized in the liver. One of the covariates is liver GVHD which
has 5 levels ( 0,1,2,3,4). The only way I can think of is to group
liver GVHD into two categories, 0 ( not GVHD) and 1 ( having GVHD).
But there is interest to evaluate the effect of degree of GVHD on pk
parameter, e.g. CL.
Does anyone have any suggestions on building a categorical covariate
model of more than two levels. Thanks for any input.
Best regards,
Hong Li, Ph.D.
Postdoctoral Associate
Department of Pharmaceutical Science
University at Buffalo, SUNY
363 Hochstetter Hall
Buffalo, NY 14260
Tel#: (716)645-4827
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