An Overview of the CLASS, CONTRAST, and HAZARDRATIO Statements in the SAS 9.2 PHREG Procedure

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The PHREG procedure fits a number of models collectively known as Cox regression models, including the well-known Cox proportional hazards model. This paper provides an overview of several new features, including three new statements (CLASS, CONTRAST, and HAZARDRATIO) in PROC PHREG. The emphasis is on illustrative examples of comparisons for main effects and interaction models via the new statements. The paper concentrates on common CLASS variable parameterization methods such as reference coding and GLM coding. Caveats regarding CLASS variables and time (including time-dependent covariates) are also discussed.