Define Time-Dependent Covariate/Expressions

Click the Expression(s) button on the Cox Proportional Hazards Regression - Quick tab to display the Define Time-Dependent Covariates/Expressions dialog box.

Element Name Description
Add Time Covariate Displays the Enter Expression for Time Dependent Covariates dialog box, which is used to add a time-dependent covariate to the design.
Edit Time Covariate Displays the Enter Expression for Time Dependent Covariates dialog box, which is used to edit a formula for an already existing time-dependent covariate.
Remove Removes an already existing time dependent covariate from the design.
The syntax rules for the expressions are identical to those for spreadsheet formulas. In addition to the available arithmetic operators and functions, the expression interpreter recognizes the symbol t_ or T_ (i.e., letter t and the underscore) to denote the survival times. By using this symbol, you can define time-dependent covariates.
Note: Expressions that do not include the symbol T_ are not valid, since they are not a function of time, and thus do not define time-dependent covariates.