1 UK Centre for Tobacco and Alcohol Studies, School of Experimental Psychology, University of Bristol, Bristol, BS8 1TU UK; MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK. Electronic address: suzi.gage@bristol.ac.uk.
2 UK Centre for Tobacco and Alcohol Studies, School of Experimental Psychology, University of Bristol, Bristol, BS8 1TU UK; MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.
3 School of Social and Community Medicine, University of Bristol, Bristol, UK.
4 MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.