1. Nuffield Department of Primary Care Health Sciences; University of Oxford; Oxford UK
2. UK Centre for Tobacco and Alcohol Studies, National Addiction Centre; Institute of Psychiatry, Psychology & Neuroscience, King's College London; London UK
3. Department of Behavioural Science and Health; University College London; London UK
4. Tobacco Research and Treatment Center, Department of Medicine; Massachusetts General Hospital and Harvard Medical School; Boston Massachusetts USA
5. EPPI-Centre, Social Science Research Unit, UCL Institute of Education; University College London; London UK