The randomised clinical trial (RCT) is the gold standard for drug evaluation. RCTs provide the core for drug development and subsequent drug approval – often in the form of rigorously designed efficacy trials in carefully selected subjects. In fact, in- and exclusion criteria are often so restrictive that only 1–7% of patients from outpatient clinics would be eligible for trials in asthma and chronic obstructive pulmonary disease (COPD).