Michael T Lynskey1, Jo Kimber2, John Strang3. 1. Addictions Department, Institute of Psychiatry, Psychology and Neuroscience, King's College, London SE5 8BB, UK. Electronic address: michael.lynskey@kcl.ac.uk. 2. Addictions Department, Institute of Psychiatry, Psychology and Neuroscience, King's College, London SE5 8BB, UK; National Drug and Alcohol Research Centre, University of New South Wales, Sydney, NSW, Australia. 3. Addictions Department, Institute of Psychiatry, Psychology and Neuroscience, King's College, London SE5 8BB, UK.