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. 2014 Dec 18;4(12):e006171. doi: 10.1136/bmjopen-2014-006171

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Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions

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COPD exacerbation frequency during the 12-month follow-up period by (A) airflow limitation stage and (B) MRC dyspnoea grade (COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 s; MRC, Medical Research Council).