Sample size estimation for a time-to-event outcome

This online sample size calculator for clinical trials involving survival (time-to-event) data assumes an exponential survival distribution. Its estimates are generally fairly close to those obtained using the proportional hazards approach and it is suitable for many common survival analysis problems.

Parameters

Significance threeshold (α)	0.025	0.05	0.10	0.20
	One-sided		Two-sided
Power (1 - β)	0.975	0.95	0.90	0.80
Incidence rate (control group)^*†
Please precise the unit	/ 100 000	/ 1000	%	Probability
Risk ratio^*
Risk in the intervention group / risk in the control group
Recruitment duration^*†
Time between the recruitment of the first and the last subject Leave blank or enter 0 if the same fixed follow-up duration is planned for all subjects.
Study duration^*†
Time between the recruitment of the first subject and the end of the study. If the same fixed follow-up duration is planned for all subjects, enter that duration.
^* You may enter multiple values, delimited by commas or spaces. ^† The time unit should by the same for the incidence rate, the recruitment duration and the study duration.

Reference

Machin D, Campbell MJ, Fayers PM, Pinol A. Sample size tables for clinical studies. Oxford, Blackwell Publications, 1996.

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