We all know that sizing a study is a critical part of trial design but unless you consider the shape of your curves you may be performing a study that is much larger than it needs to be. The size of a study depends on the desired hazard ratio (HR), which in turn governs the number of events that need to be observed to guarantee power. In practice, we often choose the desired HR, or alternative hypothesis, by considering the absolute benefit it’s likely to correspond to – stan