- Correspondence to Dr Pamela M Ling, Center for Tobacco Control Research and Education University of California, San Francisco, 350 Parnassus Ave. suite 366, San Francisco, CA 94143-1390, USA;
- Received July 5, 2013
- Revised November 13, 2013
- Accepted December 10, 2013
- First published January 21, 2014.
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