INTERVAL Subcommand (SURVIVAL command)

INTERVAL determines the period of time to be examined and how the time will be grouped for the analysis. The interval specifications apply to all of the survival variables listed on TABLE.

  • SURVIVAL always uses 0 as the starting point for the first interval. Do not specify the 0. The INTERVAL specification must begin with the keyword THRU.
  • Specify the terminal value of the time period after the keyword THRU. The final interval includes any observations that exceed the specified terminal value.
  • The grouping increment, which follows the keyword BY, must be in the same units as the survival variable.
  • The period to be examined can be divided into intervals of varying lengths by repeating the THRU and BY keywords. The period must be divided in ascending order. If the time period is not a multiple of the increment, the endpoint of the period is adjusted upward to the next even multiple of the grouping increment.
  • When the period is divided into intervals of varying lengths by repeating the THRU and BY specifications, the adjustment of one period to produce even intervals changes the starting point of subsequent periods. If the upward adjustment of one period completely overlaps the next period, no adjustment is made and the procedure terminates with an error.

Example

SURVIVAL TABLE = MOSFREE BY TREATMNT(1,3)
  /STATUS = PRISON(1) FOR MOSFREE
  /INTERVAL = THRU 12 BY 1 THRU 24 BY 3.
  • INTERVAL produces life tables computed from 0 to 12 months at one-month intervals and from 13 to 24 months at three-month intervals.

Example

SURVIVAL  ONSSURV BY TREATMNT (1,3)
  /STATUS = OUTCOME (3,4) FOR ONSSURV
  /INTERVAL = THRU 50 BY 6.
  • On the INTERVAL subcommand, the value following BY (6) does not divide evenly into the period to which it applies (50). Thus, the endpoint of the period is adjusted upward to the next even multiple of the BY value, resulting in a period of 54 with 9 intervals of 6 units each.

Example

SURVIVAL  ONSSURV BY TREATMNT (1,3)
  /STATUS = OUTCOME (3,4) FOR ONSSURV
  /INTERVAL = THRU 50 BY 6 THRU 100 BY 10 THRU 200 BY 20.
  • Multiple THRU and BY specifications are used on the INTERVAL subcommand to divide the period of time under examination into intervals of different lengths.
  • The first THRU and BY specifications are adjusted to produce even intervals as in the previous example. As a result, the following THRU and BY specifications are automatically readjusted to generate 5 intervals of 10 units (through 104), followed by 5 intervals of 20 units (through 204).