- Correspondence to Kieran J Rothnie, Respiratory Epidemiology, Occupational Medicine and Public Health, National Heart and Lung Institute, Emmanuel Kaye Building, Imperial College London, London SW3 6LR, UK;
- Received January 25, 2016
- Revised April 15, 2016
- Accepted April 21, 2016
- First published May 13, 2016.
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