The aim of this article is to revise some of the key concepts related to randomised controlled trials used to demonstrate the efficacy of harmacological treatments: the role of bias, the role of chance, clinical relevance, the external validity of trials, surrogate and composite endpoints, analysis of secondary endpoints and subgroups, non-inferiority trials, the influence of individual studies in meta-analysis and finally, the opinion of the patient.

Authors:

• Idoia Gaminde. Teaching and Education Services and Health Development. Health Department. Government of Navarre. Spain.
• Juan Erviti. Drug Information Unit. Navarre Regional Health Service. Spain.