Biostatistics For Dummies

Chapter 23

Comparing Survival Times

In This Chapter

Using the log-rank test to compare two groups

Thinking about more complicated comparisons

Calculating the necessary sample size

The life table and Kaplan-Meier survival curves described in Chapter 22 are ideal for summarizing and describing the time to the first (or only) occurrence of some event, based on times observed in a sample of subjects. They correctly incorporate censored data (when a subject isn’t observed long enough to experience the event). Animal studies or human studies involving endpoints that occur on a short time-scale (like duration of labor) might yield totally uncensored data, but most clinical studies will contain at least some censored observations.

In biological research (and especially in clinical trials), you often want to compare survival times between two or more groups of subjects. This chapter describes an important method — the log-rank test — for comparing survival between two groups and explains how to calculate the sample size you need to have sufficient statistical power (see Chapter 3) when performing this test. The log-rank test can be extended to handle three or more groups of subjects, but ...