I’ve run cause-specific Cox models and tested for multiplicative interaction (binary exposure, ordinal covariate, quintiles) and also want to test for additive interaction. I need some help figuring out how to 1) get the information I need to calculate RERI, AP, Synergy Index including confidence intervals.

I saw the paper by Li et al, but the example they give does not involve an ordinal variable. I need help figuring out how to get the information I need for my situation (ordinal x binary variable) interaction. I need to do this in SAS- R is not an option.