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SPSS® 12.0 Command Syntax Reference

SPSS® 12.0 Command Syntax Reference

SPSS® 12.0 Command Syntax Reference

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296 COXREG<br />

Example<br />

TIME PROGRAM.<br />

COMPUTE Z=AGE + T_.<br />

COXREG SURVIVAL WITH Z<br />

/STATUS SURVSTA EVENT (1).<br />

• TIME PROGRAM defines the time-dependent covariate Z as the current age. Z is then specified as<br />

a covariate.<br />

• The dependent variable SURVIVAL contains the length of time to the terminal event or to<br />

censoring.<br />

• A value of 1 on the variable SURVSTA indicates an event.<br />

TIME PROGRAM <strong>Command</strong><br />

TIME PROGRAM is required to define time-dependent covariates. These are covariates whose<br />

values change during the course of the study.<br />

• TIME PROGRAM and the transformations that define the time-dependent covariate(s) must<br />

precede the COXREG command.<br />

• A time-dependent covariate is a function of the current time, which is represented by the<br />

special variable T_.<br />

• The working data file must not have a variable named T_. If it does, rename the variable<br />

before you run the COXREG command. Otherwise, you will trigger an error.<br />

• T_ cannot be specified as a covariate. Any other variable in the TIME PROGRAM can be<br />

specified on the covariate list.<br />

• For every time-dependent covariate, values are generated for each valid case for all uncensored<br />

times in the same stratum that occur before the observed time. If no STRATA<br />

subcommand is specified, all cases are considered to belong to one stratum.<br />

• If any function defined by the time program results in a missing value for a case that has<br />

no missing values for any other variable used in the procedure, COXREG terminates with<br />

an error.<br />

CLEAR TIME PROGRAM <strong>Command</strong><br />

CLEAR TIME PROGRAM deletes all time-dependent covariates created in the previous time<br />

program. It is primarily used in interactive mode to remove temporary variables associated with<br />

the time program so that you can redefine time-dependent covariates for the Cox Regression<br />

procedure. It is not necessary to use this command if you have already executed COXREG. All<br />

temporary variables created by the time program are automatically deleted.

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