HI, I have come across an issue regarding overlapping cohorts two time-dependent eras.   I want to see if a specific time period (Era 1 vs Era 2) has affected patients waiting on a list for heart transplant.   However, the patients in Era 1 overlap into Era 2. I do not want to exclude the patients who overlap into Era 2.    Is there way that SAS to do a multivariate cox regression analysis that will allow for these overlapping cohorts when looking at the effect of an Era (Era 1 vs Era 2). ... View more