[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?


Thank you,


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