1. Massachusetts General Hospital and Harvard Medical School; Tobacco Research and Treatment Center, Department of Medicine; S50-9 Boston Massachusetts USA 02114
2. University of Lausanne; Department of Ambulatory Care and Community Medicine; Rue du Bugnon 44 Lausanne Switzerland 1011
3. Massachusetts General Hospital and Harvard Medical School; Tobacco Research and Treatment Center; 9th Floor 50 Staniford Street Boston Massachusetts USA 02114
4. University of Bristol; Department of Experimental Psychology; 8 Woodland Road Bristol UK BS8 1TN
5. University of Oxford; Department of Primary Care Health Sciences; 23-38 Hythe Bridge Street Oxford UK OX1 2ET