Medically treated exacerbations in COPD by GOLD 1-4: A valid, robust, and seemingly low-biased definition

Compared to individuals with GOLD 1, the risk of exacerbations was 17-fold for GOLD 4, 5-fold for GOLD 3, and 2-fold for GOLD 2. Medically treated exacerbations defined by register linkage seem a valid, robust, and low-biased measure of exacerbations in COPD.