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. 2012 Feb 3;7(2):e31617. doi: 10.1371/journal.pone.0031617

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Lau 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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The scatter plot of the relation between plasma 5-HT levels and age in healthy non-smokers (A), healthy ever-smokers (B) and COPD ever-smokers (C). The Spearman correlation coefficient (r) and the p value were shown.