RE: categorical covariate with 5 levels
Dear Hong,
I usually use below script for covariates with more than two (n) levels.
Please create n-1 indicator variables.
;GVHD1 = 1 for GVHD=1, 0 otherwise
GVHD1=0
IF (GVHD.EQ.1) GVHD1=1
;GVHD2 = 1 for GVHD=2, 0 otherwise
GVHD2=0
IF (GVHD.EQ.2) GVHD2=1
;GVHD3 = 1 for GVHD=3, 0 otherwise
GVHD3=0
IF (GVHD.EQ.3) GVHD3=1
;GVHD4 = 1 for GVHD=4, 0 otherwise
GVHD4=0
IF (GVHD.EQ.4) GVHD4=1
CL = THETA(A) + THETA(B)*GVHD1 + THETA(C)*GVHD2 + THETA(D)*GVHD3+
THETA(E)*GVHD4 (Additive effect of GVHD on CL)
Or
CL = THETA(A) * (1+THETA(B)*GVHD1) * (1+THETA(C)*GVHD2) * (1+THETA(D)*GVHD3) *
(1+THETA(E)*GVHD4) (Proportional shift in CL for GVHD)
Regards,
Yoshi
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Yoshimasa Ishida
Chugai Pharmaceutical CO., LTD.
Clinical PK/PD Analysis Group
Clinical Research Planning Dept.
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Quoted reply history
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Hong Li
Sent: Friday, July 09, 2010 1:01 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