Pocock Method
A Pocock design with four looks judges its final analysis at p = 0.01823. A p of 0.03 at the end is not significant.
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O’Brien–Fleming (OBF) Method
At 25% information the example needs z = 4.049. Under its target effect, 0.39% of simulated trials stop at that look.
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Group Sequential Testing
Pocock uses 71.8% of the data and gives up eight points of power. O’Brien-Fleming gives up one for a smaller saving.