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Randomised controlled trials (RCTs) are universally considered as the gold standard for evaluating the efficacy of treatments. Their main strength is that, through randomisation, they avoid any major imbalance between compared groups: therefore, observed outcome differences between groups at the end of the trial are most likely related to treatment effects. Since they are inherently prospective by design, they also permit stability throughout the study to ensure that all conditions remain optimal to test the hypothesis of interest. These include high-quality follow-up, reinforced adherence, etc . Consequently, these studies can reach the highest level of internal validity, provided that all quality standards are followed, such as those defined by CONSORT guidelines 1. This document has been Endorsed by the International Primary Care Respiratory Group and the World Allergy Organization. The authors wish to thank the Respiratory Effectiveness Group Team (Michael Walker, CEO and Supporter Liaison, Naomi Launders, Senior Scientific Researcher and Sarah Lucas, Researcher) and Oversight Committee (Keith Allan, Trevor Lambert and Nick May).
Roche et al. (Sun,) studied this question.