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 developing 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 calculation given your research question and context.