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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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1548 SURVIVAL<br />

Operations<br />

• SURVIVAL computes time intervals according to specified interval widths, calculates the<br />

survival functions for each interval, and builds one life table for each group of survival<br />

variables. The life table is displayed unless explicitly suppressed.<br />

• When the PLOT subcommand is specified, SURVIVAL plots the survival functions for all<br />

cases or separately for various groups.<br />

• When the COMPARE subcommand is specified, SURVIVAL compares survival-time<br />

distributions of different groups based on the Wilcoxon (Gehan) statistic.<br />

Limitations<br />

Example<br />

• Maximum 20 survival variables.<br />

• Maximum 100 control variables total on the first- and second-order control-variable lists<br />

combined.<br />

• Maximum 20 THRU and BY specifications on INTERVALS.<br />

• Maximum 35 values can appear on a plot.<br />

SURVIVAL TABLES=MOSFREE BY TREATMNT(1,3)<br />

/STATUS = PRISON (1) FOR MOSFREE<br />

/INTERVALS = THRU 24 BY 3.<br />

• The survival analysis is used to examine the length of time between release from prison<br />

and return to prison for prisoners in three treatment programs. The variable MOSFREE is<br />

the length of time in months a prisoner stayed out of prison. The variable TREATMNT<br />

indicates the treatment group for each case.<br />

• A value of 1 on the variable PRISON indicates a terminal outcome—that is, cases coded<br />

as 1 have returned to prison. Cases with other non-negative values for PRISON have not<br />

returned. Because we don’t know their final outcome, such cases are called censored.<br />

• Life tables are produced for each of the three subgroups. INTERVALS specifies that the<br />

survival experience be described every three months for the first two years.<br />

TABLES Subcommand<br />

TABLES identifies the survival and control variables to be included in the analysis.<br />

• The minimum specification is one or more survival variables.<br />

• To specify one or more first-order control (or factor) variables, use the keyword BY<br />

followed by the control variable(s). First-order control variables are processed in<br />

sequence. For example, BY A(1,3) B(1,2) results in five groups ( A = 1 , A = 2 ,<br />

A = 3 , B = 1 , and B =<br />

2 ).<br />

• You can specify one or more second-order control variables following a second BY<br />

keyword. Separate life tables are generated for each combination of values of the firstorder<br />

and second-order controls. For example, BY A(1,3) BY B(1,2) results in six

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