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 _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ Yoshimasa Ishida Chugai Pharmaceutical CO., LTD. Clinical PK/PD Analysis Group Clinical Research Planning Dept. _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ -----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
