Editorial

Editorial on hypothesis and objectives in clinical trials: superiority, equivalence and non-inferiority

Claudio D Gonzalez¹ , Ricardo Bolaños¹ and Martha de Sereday²

¹  Department of Pharmacology, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina

²  Committee of Epidemiology, Argentinean Society of Diabetes, Buenos Aires, Argentina

author email corresponding author email

Thrombosis Journal 2009, 7:3doi:10.1186/1477-9560-7-3

Published:	21 March 2009

First paragraph (this article has no abstract)

Randomized clinical trial is often considered as the Gold Standard method for comparing treatment effects. In practice, taking into consideration their main objectives, the majority of clinical trials are aimed to establish the superiority of an intervention regarding to an active control or placebo [1]. Within the methodological core of these so called superiority trials, the assessment of the statistical signification of the differences between or among interventions, and their clinical relevance, are both of main importance. Appropriate statistical tests to assess this superiority should be performed, with the null hypothesis being: the difference between treatments is equal to 0 (H0 ≡ Δ = 0), and the alternative hypothesis: treatments are different -or, the difference between treatments is not equal to 0 (H1 ≡ Δ ≠ 0)(if two sided)-. The rejection of the null hypothesis is in the foundation of the methodological assessment of superiority [2]. The number of patients required to confront the hypotheses is inversely related to the expected between-treatment differences. The smallest the expected difference between two interventions, the highest the number of patients to be included into the trial. But, how to interpret a non-significant result obtained from a clinical study designed as a superiority trial? Does this mean that the interventions under study should be considered as equivalent?. Clearly, the answer is negative. From the methodological standpoint, the expression: we have no evidence of difference between treatments, should not be considered as equivalent to: we have evidence of no difference between interventions [3].