The validity of International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes for identifying patients hospitalized for COPD exacerbations - Stein, BD; Bautista, A; Schumock, GT; Lee, TA; Charbeneau, JT; Lauderdale, DS; Naureckas, ET; Meltzer, DO; Krishnan, JA (Chest, 2012)