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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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STRATA Subcommand<br />

KM 791<br />

STRATA identifies a stratification variable—that is, a variable whose values are used to<br />

form subgroups (strata) within the categories of the factor variable. Analysis is done within<br />

each level of the strata variable for each factor level, and estimates are pooled over strata for<br />

an overall comparison of factor levels.<br />

• The minimum specification is the subcommand keyword with one, and only one, variable<br />

name.<br />

• If you have more than one strata variable, create a new variable to combine the levels on<br />

separate variables before invoking the KM command.<br />

• There is no limit to the number of levels for the strata variable.<br />

Example<br />

KM LENGTH BY SEXRACE<br />

/STATUS=EMPLOY EVENT (1) LOST (3,5 THRU 8)<br />

/STRATA=LOCATION.<br />

• STRATA specifies LOCATION as the stratification variable. Analysis of the length of<br />

unemployment is done for each location within each sex and race subgroup.<br />

PLOT Subcommand<br />

PLOT plots the cumulative survival distribution on a linear or logarithmic scale or plots the<br />

cumulative hazard function. A separate plot with all factor levels is produced for each stratum.<br />

Each factor level is represented by a different symbol or color. Censored cases are indicated<br />

by markers.<br />

• When PLOT is omitted, no plots are produced. The default is NONE.<br />

• When PLOT is specified without a keyword, the default is SURVIVAL. A plot of survival<br />

functions for each stratum is produced.<br />

• To request specific plots, specify, following the PLOT subcommand, any combination of<br />

the keywords defined below.<br />

• Multiple keywords can be used on the PLOT subcommand, each requesting a different<br />

plot. The effect is cumulative.<br />

SURVIVAL Plot the cumulative survival distribution on a linear scale. SURVIVAL is the<br />

default when PLOT is specified without a keyword.<br />

LOGSURV Plot the cumulative survival distribution on a logarithmic scale.<br />

HAZARD Plot the cumulative hazard function.<br />

OMS Plot the one-minus-survival function.<br />

Example<br />

KM LENGTH BY SEXRACE<br />

/STATUS=EMPLOY EVENT (1) LOST (3,5 THRU 8)<br />

/STRATA=LOCATION<br />

/PLOT = SURVIVAL HAZARD.<br />

• PLOT produces one plot of the cumulative survival distribution on a linear scale and one<br />

plot of the cumulative hazard rate for each value of LOCATION.

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