Survival Analysis Using SAS®: A Practical Guide

Categorical Variables and the CLASS Statement

In the recidivism example, several of the covariates—race, marital status, work experience, and parole status—are dichotomous variables that are coded as indicator (dummy) variables. For categorical covariates with more than two categories, the standard approach is to create a set of indicator variables, one for each category (except for one). You can do this in the DATA step, but PROC LIFEREG does it automatically if the variable (or variables) is listed in a CLASS statement. Here’s an example. Another covariate in the recidivism data set is education, which was originally coded like this:

2 = 6th grade or less	24 cases
3 = 7th to 9th grade	239 cases
4 = 10th to 11th grade	119 cases
5 = 12th grade	39 cases ...