I have a very general question about what the centering option in basehaz does to factors.  (basehaz computes the baseline cumulative hazard for a coxph object using the Breslow estimator).

Lets say I'm interested in a survival model with two (dichotomous) factors and a continuous covariate.
Variable               Possible Values
Factor1                0 or 1
Factor2                0 or 1
Covariate            0 to 100

I fit my model:
modelname <- coxph(Surv ~ Factor1 + Factor2 + Covariate, data = data)

If I then ask for:
baselineA <- basehaz(modelname, centered=FALSE)
I am fairly certain that baselineA will provide me with the cumulative hazard evaluated at Factor1 = 0, Factor2 = 0, Covariate = 0.

Yet, if I ask for:
baselineB <- basehaz(modelname, centered=TRUE)
I know that baselineB will evaluate the cumulative hazard at Covariate = 50, but am uncertain as to what it does with the factors.  I would not think that the function would attempt to average a "factor"; however, I cannot find any documentation to support my assumption.  To make sure, does anyone know how basehaz (centered = TRUE/FALSE) handles models that include both categorical factors and continuous covariates?

Thanks in advance,
Dave Koons

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