Dendreon Corp fka DNDNQ

[iwfal]

As a result, an interim look with a substantially lower number of events is not expected to be statistically significant, but if the sponsor desires an interim look (for example, to allow a cost avoiding termination of a trial for futility) and continues the trial, an alpha allocation is deducted from the normal statistical significance to account for having a second look, even though bias, post the interim look, should not be a problem in a survival trial.

This is part of the correct answer. The missing part is that the alpha is the thing they need to meet for the interim. It isn't about bias but about getting two bites at the apple.

Lets say you are testing a coin to see if it 'fair'. So you flip the coin 100 times and see if the number of heads is under p=0.05. What is the chance that a fair coin will produce such a p value? 5%.

Now for each flip use the same p calc method and calc p after each flip. What are the odds that a fair coin would at some point produce p<0.05? A lot higher than 5%. Because you had 90+ bites at the apple.

As for your questions about post hoc data mining - and the Petrylak's presentation was indisputably that - I don't really understand the question. But the chance that the FDA would give any credence to such a complicated post hoc analysis is zilch.

Clark