CATEGORICAL Subcommand (COXREG command)

CATEGORICAL identifies covariates that are nominal or ordinal. Variables that are declared to be categorical are automatically transformed to a set of contrast variables (see CONTRAST Subcommand (COXREG command)). If a variable coded as 0–1 is declared as categorical, by default, its coding scheme will be changed to deviation contrasts.

• Covariates not specified on CATEGORICAL are assumed to be at least interval, except for strings.
• Variables specified on CATEGORICAL but not on VARIABLES or any METHOD subcommand are ignored.
• Variables specified on CATEGORICAL are replaced by sets of contrast variables. If the categorical variable has n distinct values, n−1 contrast variables will be generated. The set of contrast variables associated with one categorical variable are entered or removed from the model together.
• If any one of the variables in an interaction term is specified on CATEGORICAL, the interaction term is replaced by contrast variables.
• All string variables are categorical. Only the first eight bytes of each value of a string variable are used in distinguishing among values. Thus, if two values of a string variable are identical for the first eight characters, the values are treated as though they were the same.