Let's assume that the 180th event occurs on July 1, 2008 and the DSMB unblinds for the first interim look. Let's also assume that 120 patients had enrolled by July 1, 2005, approximately two years after the first patient enrolled. Let's further assume that enrollment for the first year was linear, at 4 patients per month. The second year enrollment assumption is 6 patients per month. I wonder how much the extra time beyond three years the long-term survivors are followed would help the p value.
Looking at some of the simulations, I'm starting to wonder if it would be better for the company if the interim unblinding occurs in the 210-240 event range instead, and reserved alpha is 0.02...
