Example (CLEAR TIME PROGRAM command)

TIME PROGRAM.
COMPUTE Z=AGE + T_.

CLEAR TIME PROGRAM.

TIME PROGRAM.
COMPUTE Z=AGE + T_ - 18.

COXREG SURVIVAL WITH Z
  /STATUS SURVSTA EVENT(1).

• The first TIME PROGRAM command defines the time-dependent covariate Z as the current age.
• The CLEAR TIME PROGRAM command deletes the time-dependent covariate Z.
• The second TIME PROGRAM command redefines the time-dependent covariate Z as the number of years since turning 18.. Z is then specified as a covariate in COXREG.