Several composite indices of disease severity have been developed (table 4) [43–50]. Although the prognostic accuracy of each of these indices has been confirmed in separate studies, few studies have directly compared one index to another. The GOLD Global Strategy for the Diagnosis, Management, and Prevention of COPD [8] proposed a multidimensional assessment of COPD for the purposes of treatment selection. The assessment includes: 1) high/low symptoms using the mMRC dyspnoea scores, the COPD Assessment Test, or the clinical COPD questionnaire; 2) the severity of airflow limitation; and 3) the number of yearly exacerbations. Patients with high symptom scores (mMRC dyspnoea score ⩾2, COPD Assessment Test score ⩾10, or clinical COPD questionnaire score ⩾1) and GOLD grade 3 or 4 spirometry and/or frequent exacerbations (two or more exacerbations in the preceding year and/or one hospitalisation) are considered at high risk for further exacerbations and, indirectly, poor clinical outcomes. The proposed approach has not yet been fully validated and is the subject of current research [51–53].