Figure 3.

Severity stage and natural history of chronic obstructive pulmonary disease (COPD). Two theoretical natural histories are shown. Grouping by severity would pool a 40-year-old (patient A) with a rapidly progressive natural history (dotted line) and a 70-year-old (patient B) with a slowly progressive natural history (dashed line). Conversely, to group individuals of many ages with the rapidly progressive natural history (dotted line), individuals with differing severities (patients A and C) would need to be grouped. GOLD = Global Initiative for Chronic Obstructive Lung Disease.