Using a claims database we created a disease cohort to evaluate a safety outcome. To put it into a context, we randomly chose a non-disease cohort that was 1:1 matched with the disease cohort on age, sex, and cohort entry date (+/- 30 days), where cohort entry date was defined as the inpatient/outpatient visit date. For the disease cohort, the cohort entry date was the disease diagnosis date. We also generated a list of covariates that are risk factors for the safety outcomes. What do we need to consider when we Cox regression models to assess the hazard ratios (proc phreg) for the safety outcome for the matched disease vs non-disease cohort? Thank you very much.