Table 1.

Sample sizes for clinical trials

	N1	N2	P1	P2	Null hypothesis	Alternative hypothesis
Safety	176	176	0.10	0.20	P1 = P2	P1 < P2
	381	381	0.05	0.10	P1 = P2	P1 < P2
Efficacy on angiographic recurrences	218	218	0.10	0.20	P1 = P2	P1 <> P2*
	474	474	0.10	0.05	P1 = P2	P1 <> P2*
Efficacy regarding long-term bleeding	2021	2021	0.02	0.01	P1 = P2	P1 > P2
	4071	4074	0.01	0.005	P1 = P2	P1 > P2
Two proportions Power Analysis using one-sided or two-sided* Chi-square tests with continuity correction (a = 0.05; b = 0,20). N1 and N2 are the sample sizes necessary to demonstrate a significant difference between proportions P1 and P2; for example, 474 patients are necessary to demonstrate that the observed recurrence rate of 10% in the control group has been decreased to 5% by the new device