CHAPTER 21 Summarizing and Graphing Survival Data 311

the years from Year 1 through Year N. Because surviving each year is an indepen-

dent accomplishment, the probability of surviving all N of the years is the product

of the individual years’ probabilities. So Column H is a running product of Column G.

In other words, the value of Column H for Year N is the product of the first N

values in Column G.

Here’s to fill in Figure 22-3 (with the results shown in Figure 22-4):»

» ^{For Year 1, H is the same as G: a 0.895 probability of surviving one year.»}

» ^{For Year 2, H is the product of G for Year 1 times G for Year 2; that is, 0.895 ×}

1.000, or 0.895.»

» ^{For Year 3, H is the product of the Gs for Years 1, 2, and 3; that is, 0.895 ×}

1.000 × 0.750, or 0.671.»

» ^{Calculations continue in the same way for the remaining years.}

Putting everything together

Figure  21-4 shows the spreadsheet with the results of all the preceding

calculations.

Interpreting a life table

Figure 21-4 contains the hazard rates (in Column F) and the cumulative survival

probabilities (in Column H) for each year following surgery, based on your sample

of ten participants. Keep in mind these life-table features:»

» ^{The hazard and survival values obtained from this life table are estimates}

from a sample of the true population hazard and survival functions (in this

case, using one-year intervals).

FIGURE 21-4:

Completed life

table to analyze

the survival

times shown in

Figure 22-2.

© John Wiley & Sons, Inc.