I have data with multiple records of same ID as was captured at 0, 6, 12 and 18 months... then failure (death) was being recorded during these follow up times. how do i stset these data in STATA? i would want to do histograms for age and weight and also will fit extended cox models as i want to take care of time-varying covariates... am comparing ordinaly cox which ignore time varying covariates and survival methods that put into account time-varying covariates