Abstract: This paper deals with the principles and approaches to specify the equivalence margin in equivalence or non-inferiority trials.It is a difficult work to define equivalence boundary appropriately in clinical trials design.The selection of equivalence margin should provide assurance the effectiveness of experimental treatment relative to placebo firstly.Based on the analysis of previous studies, the statistical reasoning, clinical relevant, the choice of clinical outcome, the characteristics of particular diseases, toxicity, adverse effects, and risk-benefit assessment must be considered for equivalence margin pre-specified reasonably.

Key words: equivalence trial, clinical trial design, equivalence margin, clinical relevant