HR at the interim would have to be HR>=0.95 in order to trigger Futility
Good to see we are already 0.05 HR closer to each other. ;-) I will safely wager you the futility HR boundary will not be 1.0.
Nevertheless we can agree that while passing a futility hurdle doesn't mean the hazard ratio is great, it does say it's not on the wrong side of 1, ie harming patients. Even if it's not that much more informative, it at least limits the observed HR to below 1 be it 0.95 or 0.9. Then the non-termination for superiority then set the lower bound, somewhere at 0.71~0.72, per the OBF boundary. Without even knowing the exact the futility HR, it should be easy that we agree that if we let our simulator loose with an observed HR drawn from (0.71 to 1), the power of success at the second interim will be much higher than the 5% claimed by Martin, who essentially assumes the interim HR to be null. My question is how could he be so sure.
Now if I were to let personal bias, ie favorable view of cancer vaccine take hold, and believe regardless of the observed hazard ratio, that the true hazard ratio is as originally designed 0.6, or believing in some delayed treatment effect, which Martin fails to notice, then the power at the secodn interim will be even higher.
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