Non inferiority Margin without Placebo controlled Trial

How to estimate the Non inferiority Margin/Equivalence Margin if we do not have Placebo controlled Trial

This is not the answer you are looking for, but the tradition of determining noninferiority margins from previous studies has got to end IMHO. Non-inferiority should be based on what’s important to the patient no matter how well an active control has done in comparison to placebo previously.