Note:An SAS program would include these instructions:PROC LIFETEST METHOD = KM;
TIME WEEKS*RELAPSE(0);
STRATA DRUG;
where KM stands for the Kaplan–Meier method, WEEKS is the variable name
for duration time, RELAPSE is the variable name for survival status, ‘‘0’’ is the
coding for censoring, and DRUG is the variable name specifying groups to be
compared.
The tests above are applicable to the simultaneous comparison of several
samples; whenkgroups are to be compared, the chi-square tests, both the log-
rank and generalized Wilcoxon, haveðk 1 Þdegrees of freedom.
11.3 SIMPLE REGRESSION AND CORRELATION
In this section we discuss the basic ideas of simple regression analysis when
only one predictor or independent variable is available for predicting the sur-
vival of interest. The following example is used for illustration in this and the
following sections.
Example 11.3 A group of patients who died of acute myelogenous leukemia
were classified into two subgroups according to the presence or absence of a
Figure 11.5 Two survival curves: drug 6-MP group and placebo group.390 ANALYSIS OF SURVIVAL DATA