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Williams JE, Green RH, Warrington V, Steiner MC, Morgan MD, Singh SJ.Williams JE, et al. Among authors: singh sj.Respir Med. 2012 Mar;106(3):390-6. doi: 10.1016/j.rmed.2011.09.005. Epub 2011 Oct 5.Respir Med. 2012.PMID: 21978938Free article.