A superiority trial is a clinical trial that aims to demonstrate that an investigational medicinal product is superior to a comparator treatment (placebo, active comparator) with respect to a defined endpoint (superiority). It is the classic study design for the initial development of new active substances and forms the statistical basis of most marketing authorisation trials.
The statistical null hypothesis (H₀) states: no difference (or: the investigational medicinal product is not better than the comparator). The alternative hypothesis (H₁) states: the investigational medicinal product is superior. A statistically significant result (p < α) permits rejection of H₀ and the conclusion of superiority. The significance level (α) and the expected effect size determine the required sample size.
Non-inferiority trials (demonstrating that the investigational medicinal product is not worse than the standard – relevant for generics, biosimilars, new dosage forms) and equivalence trials (demonstrating that the investigational medicinal product is neither better nor worse than the standard) must be distinguished from this. For CROs, correct study design selection and the corresponding sample size calculation are a central biostatistical and regulatory advisory task. Regulatory reference: ICH E9, CPMP/EWP/2158/99.