The overlap in the terminology that is used to define asthma, chronic bronchitis, emphysema, COPD and bronchiectasis is the greatest cause of confusion in distinguishing these diseases and in accurately determining the prevalence of airway diseases. The prevalence of obstructive diseases in adults can vary by more than 200% in the general population and depends on the definition that is used (a self-reported diagnosis versus a diagnosis based on spirometry findings). Furthermore, the actual prevalence of obstructive diseases is underestimated. When a spirometric evaluation was performed in the general population, approximately 58% of the patients with an obstructive disorder did not report a prior lung disease diagnosis