what is sandwich estimator vs clustering model why use a sandwich model in multilevel modeling what model does a cluster in the cox proportional hazards model have why clustering in cox proportional hazards what is the mlm why use a cox proportional hazards model is sandwich a multilevel model what is sandwich estimator cox proportional hazards modeling vs sandwich estimator what is the mlm sandwich estimator used for which model can cluster patients in hospitals what modeling tool to use for clustering in cox proportional hazards model what models use sandwich estimator what is the difference between cox-pharm hazard and sandwich estimator? cox proportional hazards definition what kind of model use clustering why use cox proportional hazards what model does cox proportional hazards use what model is used for clustering mlm which lgm is sandwich estimating