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A prospective study was performed to investigate the effects of behavior type and smoking habits on heart disease. Participants were followed for nine years, and the time variable of interest was the interval (in days) from entry into the study until the appearance of coronary heart disease. Individuals were classified by two types of behavior on the basis of an interview: Type A is characterized by aggressiveness and competitiveness, and Type B is considered more relaxed and noncompetitive.

Use the plot of the survival curves to determine which behavior type yielded the more favorable “survival experiences” among the participants for the first 5 years (roughly 1825 days) of the study.

SAS Institute Inc.

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The Wcgs data set contains event time and censor variables for 614 participants, as well as measurements of two covariates of interest: smoking behavior at study entry and behavior type.

These are the variables in the data set:

This data is sample data from SAS Institute Inc.

It appears that the survival curve for the Type B behavior group lies above that of the Type A behavior group from time = 0 days to about time = 2850 days. So, we can say that the more relaxed, noncompetitive individuals had a more favorable survival experience for the first 5 years of the study.