Fig. 2

Showing three different group sequential boundaries in a single trial with interim analysis. The Z-value is the test statistic and a |Z| = 1.96 corresponds to P = 0.05; the higher the Z-value, the lower the P-value. This is a historical overview of group sequential boundaries for the cumulative Z-curve in relation to the number of randomised participant in a single trial [19, 32, 33]