User Guide

Chapter 9

Statistics. Number entering, number leaving, number exposed to risk, number of

terminal events, proportion terminating, proportion surviving, cumulative proportion

surviving (and standard error), probability density (and standard error), and hazard rate

(and standard error) for each time interval for each group; median survival time for

each group; and Wilcoxon (Gehan) test for comparing survival distributions between

groups. Plots: function plots for survival, log survival, density, hazard rate, and one

minus survival.

Data. Your time variable should be quantitative. Your status variable should be

dichotomous or categorical, coded as integers, with events being coded as a single

value or a range of consecutive values. Factor variables should be categorical, coded as

integers.

Assumptions. Probabilities for the event of interest should depend only on time after the

initial event—they are assumed to be stable with respect to absolute time. That is, cases

that enter the study at different times (for example, patients who begin treatment at

different times) should behave similarly. There should also be no systematic

differences between censored and uncensored cases. If, for example, many of the

censored cases are patients with more serious conditions, your results may be biased.

Related procedures. The Life Tables procedure uses an actuarial approach to this kind

of analysis (known generally as Survival Analysis). The Kaplan-Meier Survival

Analysis procedure uses a slightly different method of calculating life tables that does

not rely on partitioning the observation period into smaller time intervals. This method

is recommended if you have a small number of observations, such that there would be

only a small number of observations in each survival time interval. If you have

variables that you suspect are related to survival time or variables that you want to

control for (covariates), use the Cox Regression procedure. If your covariates can have

different values at different points in time for the same case, use Cox Regression with

Time-Dependent Covariates.

To Create a Life Table

 From the menus choose:

Analyze

Survival

Life Tables…