Could you please explain this? How is final alpha 0.045 with no interims? Why is it not .05 (.025 one-sided)?
ONTY has given us enough information that we can calculate the-final-alpha-if-there-were-no-interims. That calculation uses as input the Assumed HR (=20/26), the number of events for the final trigger (705), the power (90%) and the enrollment ratio (2). That final alpha is somewhere between 0.045 and 0.047 or so - depending upon how Merck did the calculation (credit to AVII here for noting that the different formulas for powering produce slightly different numbers).
But note that even that small amount of missing alpha translates into a non-trivial amount of alpha for the aggregate interims (because the 75% interim and the final share so many events they get to 'share' some of the same alpha - so a missing 0.005 translates into about 0.015 at 75% information fraction). It is not precise enough a calculation to prove that the interims were OBF - but it is good enough to indicate that they were probably well above 0.002 each (the numbers from Wedbush).
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