title: How to demonstrate similarity by using noninferiority and equivalence statistical testing in radiology research.
abstract: Demonstrating similarity between compared groups--that is, equivalence or noninferiority of the outcome of one group to the outcome of another group--requires a different analytic approach than determining the difference between groups--that is, superiority of one group over another. Neither a statistically significant difference between groups (P < .05) nor a lack of significant difference (P ≥ .05) from conventional statistical tests provides answers about equivalence/noninferiority. Statistical testing of equivalence/noninferiority generally uses a confidence interval, where equivalence/noninferiority is claimed when the confidence interval of the difference in outcome between compared groups is within a predetermined equivalence/noninferiority margin that represents a clinically or scientifically acceptable range of differences and is typically described by Δ. The equivalence/noninferiority margin should be justified both clinically and statistically, considering the loss in the main outcome and the compensatory gain, and be chosen conservatively to avoid making a false claim of equivalence/noninferiority for an inferior outcome. Sample size estimation needs to be specified for equivalence/noninferiority design, considering Δ in addition to other general factors. The need for equivalence/noninferiority research studies is expected to increase in radiology, and a good understanding of the fundamental principles of the methodology will be helpful for conducting as well as for interpreting such studies.
authors.affiliation: Medical Research Collaborating Center and Department of Radiology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Gyeonggi-do, Korea.
authors.forename: Soyeon
authors.initials: S
authors.lastname: Ahn
authors.forename: Seong Ho
authors.initials: SH
authors.lastname: Park
authors.forename: Kyoung Ho
authors.initials: KH
authors.lastname: Lee
mesh_terms: D035843:Biomedical Research; D003627:Data Interpretation, Statistical; D006801:Humans; D011871:Radiology; D012107:Research Design; D018401:Sample Size