I have been reading up on group sequential clinical trial designs and came across the concept of non-binding futility boundaries. Intuitively, it makes sense to me that continuing the trial after crossing a binding futility boundary would increase your chances of a Type-I error--hence, the need to develop methods for a non-binding boundary.
But there seems to be no discussion/mention of non-binding efficacy boundaries. It makes sense that continuing after crossing the efficacy boundary wouldn't affect Type-I error but it would increase Type-II error (and thus, decrease power). The fact that this is not discussed anywhere makes me think that I'm missing something obvious/there's a glaring gap in my knowledge. I would appreciate some insight into this.
