332 PART 6 Analyzing Survival Data

To understand the flex, look at what happens when you raise this straight line to

various powers, which we refer to as h and illustrate in Figure 23-1b:»

» ^{Squaring: If you set h = 2, the y value for every point on the line always comes}

out smaller, because they are always less than 1. For example, 0 8²

.

is 0.64.»

» ^{Taking the square root: If we set h = 0.05, the y value of every point on the}

line becomes larger. For example, the square root of 0.25 is 0.5.

Notice in Figure 23-1b, both 1² and 1^{0 5.} remain 1, and 0² and 0^{0 5.} both remain 0, so

those two ends of the line don’t change.

Does the same trick work for a survival curve that doesn’t follow any particular

algebraic formula? Yes, it does! Look at Figure 23-2.

FIGURE 23-1:

Bending a

straight line into

different shapes

by raising each

point on the line

to some power: h.

© John Wiley & Sons, Inc.

FIGURE 23-2:

Raising to a

power works

for survival

curves, too.

© John Wiley & Sons, Inc.