So I don't get it. There's no data on interims in the calculation whatsoever. You put in the powering assumptions (90%, 20 vs 26, 2:1, .025 one-sided) and it tells you you need 705 events at the final look. How can that possibly tell you anything about alpha spent on interims? Where is the impact of the interim structure on this outcome?
This is a learning exercise, I think you would agree.
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