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. 2014 Jun 27;9(6):e101228. doi: 10.1371/journal.pone.0101228

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© 2014 Blasi et al

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.

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Group A: patients with at least one severe exacerbation of chronic obstructive pulmonary disease (E-COPD) in the three-year pre-index period; Group B: patients with only moderate E-COPD in the three-year pre-index period; Group C patients without E-COPD in the three-year pre-index period. Differences between groups are significant (p<0.05, Log-rank and Wilcoxon tests).