Uncertainty in study planning

Background

A phase III cardiovascular superiority study is planned with the following assumptions (simplified, no lost-to-FU, no treatment discontinuation, no non-CV death):

• Hazard rate of active comparator 5% per year
• Hazard ratio 0.775
• Accrual time 24 months, total duration 30 months

Statistical settings:

• Logrank test for superiority in time to first MACE event (CV death, MI, stroke)
• Alpha 5%, Power 90%
• A sample size of about 9900 patients would be needed aiming for 650 patients experiencing a MACE event to show superiority of the new treatment over the comparator in reducing MACE events.

Challenge

How can uncertainty be displayed with regard to total study duration if the assumptions are not exactly met, i.e. comparator hazard rate between 4% and 6% (and hazard ratio between 0.75 and 0.8)?