Biotech Values

[iwfal]

I will safely wager you the futility HR boundary will not be 1.0.

If they used 20% conditional power (a threshold suggested in one of my text books) I am pretty sure it would be an interim HR>1.0 (using OBF at 50% info fraction). I just don't know what threshold gets it under 1.0.

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.

I'll acknowledge that Martin didn't put his story together in a completely coherent way - but I believe his thesis is that the drug is no better than placebo, and given this assumption then even if it passed the interim futility analysis then it is still has odds of less than 5% (when, prior to the interim, the odds of success for a worthless treatment were 2.5%). That said, upon further thought I will amend my previous statement to just say that 5% is roughly correct given those assumptions.