[R] Centring variables in Cox Proportional Hazards Model
Laura Bonnett
l.j.bonnett at googlemail.com
Thu Mar 26 12:31:11 CET 2009
Dear All,
I am contemplating centering the covariates in my Cox model to reduce
multicollinearity between the predictors and the interaction term and
to render a more meaningful interpretation of the regression
coefficient. Suppose I have two indicator variables, x1 and x2 which
represent age categories (x1 is patients less than 16 while x2 is for
patients older than 65). If I use the following Cox model, is there
anyway I can centre the variables? Do I have to do it before I fit
them into the model and if so, how?
fit2=coxph(Surv(rem.Remtime,rem.Rcens)~x1(partial)+x2(partial),data=partial,method="breslow")
Thank you,
Laura
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