CHAPTER 22 Comparing Survival Times 321

In Figure 22-2, the Drug group’s results are in columns B through E, and the Con-

trol group’s results are in columns F through I. The only measurements needed

from Figure 22-2 for the log-rank test are At risk (columns E and I), meaning

number at risk in each time slice for each group, and Died (columns C and G),

meaning the number of observed deaths in that time slice for each group. The log-

rank test calculations are in a second spreadsheet (shown in Figure 22-3).

The spreadsheet shown in Figure 22-3 has the following columns:»

» ^{Column A identifies the time slices, consistent with Figure 22-2.»}

» ^{Columns B and C pertain to the Drug group, and reprint the At risk and Died}

columns from Figure 22-2 for that group. Columns D and E pertain to the

Control group and reprint the At risk and Died columns from Figure 22-2 for

that group.»

» ^{Columns F and G show the combined total number of individuals at risk and}

the total number of individuals who died, which is obtained by combining the

corresponding columns for the two groups.»

» ^{Column H, labeled % At Risk, shows Group 1’s percentage of the total number}

of at-risk individuals per time slice.

FIGURE 22-2:

A portion of the

life-table

calculations for

two groups of

laboratory

animals.

© John Wiley & Sons, Inc.

FIGURE 22-3:

Basic log-rank

calculations done

manually (but

please use

software

instead!).

© John Wiley & Sons, Inc.