Steve - I don't even know what it means to have a minimum hazard ratio to meet stat sig. But, since the hazard ratio is a measure of drug benefit, if it gets too low, then who cares if the trial meets stat sig anyway.
The real question is how to model the data so that any prediction from that would be trustworthy. As I mentioned a few times already, if you assume 240 as the trigger and only D9901+02a as the model, then the chance of success is about 50%.
But we know that the early phase of IMPACT enrolled much better patients than D9901, ie, the GS<=7 patients. I estimated that the GS<=7 patients could make up about 2/3 or more of IMPACT. That's much better than the 59-60% in D9901 or D9902a. If you go back to the Jan 2004 PR on the survival data of D9901, these patients exhibited an HR of 1.89.
Now, I suspect that the latter phase of IMPACT, especially after the CRL, when they tried to finish enrollment might include much sicker patients (caseystarman's friend is probably a good example). So in any simulation work, this effect should be taken into account.
Over all, my personal belief (and it is that, just a belief) is that IMPACT will turn out better than the integrated data. How much better is an open question and that, in turn, put into question the chance of the interim success. But I think that chance is better than 50%.
