Survival Analysis Using SAS®: A Practical Guide

Introduction

This chapter shows how to use the LOGISTIC, PROBIT and GENMOD procedures to analyze data in which many events occur at the same points in time. In Chapter 5, “Estimating Cox regression Models with PROC PHREG,” we looked at several different methods for handling tied data with PROC PHREG. There we saw that Breslow’s method—the standard formula for partial likelihood estimation with tied data—is often a poor approximation when there are many ties. This problem was remedied by two exact methods, one that assumed that ties result from imprecise measurement and another that assumed that events really occur at the same (discrete) time. Unfortunately, both of these methods are computationally demanding for large data sets with many ties. ...