Noninferiority and equivalence designs: issues and implications for mental health research.

The terms noninferiority and equivalence are often used interchangeably to refer to trials in which the primary objective is to show that a novel intervention is as effective as the standard intervention. The use of these designs is becoming increasingly relevant to mental health research. Despite the fundamental importance of these designs, they are often poorly understood, improperly applied, and subsequently misinterpreted. In this article, the authors explain noninferiority and equivalence designs and key methodological and statistical considerations. Decision points in using these designs are discussed, such as choice of control condition, determination of the noninferiority margin, and calculation of sample size and power. With increasing utilization of these designs, it is critical that researchers understand the methodological issues, advantages, disadvantages, and related challenges.