CHAPTER 23 Survival Regression 347

You still have to specify the following:»

» ^{Desired α level: We recommend 0.05»}

» ^{Desired power: We usually use 80 percent»}

» ^{Effect size of importance: This is typically expressed as a HR or as the}

difference in median survival time between groups

You also need estimates of the following:»

» ^{Anticipated enrollment rate: How many participants you hope to enroll per}

time period»

» ^{Planned duration of follow-up: How long you plan to continue following all}

the participants after the last participant has been enrolled before ending the

study and analyzing your data

If you are uncomfortable with estimating sample size for a large study that will be

evaluated with a regression model, consult a statistician with experience in devel-

oping sample-size estimates for similarly-designed studies. They will be able to

guide you in the tips and tricks they use to arrive at an adequate sample-size cal-

culation given your research question and context.