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. 2021 Nov 30;11(11):e053684. doi: 10.1136/bmjopen-2021-053684

Table 3.

Interim analysis sample size calculation for a binary endpoint

Stage 1 2
Information rate 50% 100%
Efficacy boundary (z-value scale) 2.963 1.969
Overall power 0.1641 0.8000
No of subjects 61.8 123.7
Cumulative alpha spent 0.0031 0.0500
Two-sided local significance level 0.0031 0.0490
Lower efficacy boundary (t) −0.377 −0.172
Upper efficacy boundary (t) 0.277 0.148

Sequential analysis with a maximum of 2 looks (group sequential design). The sample size was calculated for a two-sample test for rates (two sided), H0: pi(1) − pi(2) = 0, H1; treatment rate pi(1) = 0.9, control rate pi(2) = 0.7. (t): approximate treatment effect scale.