Charles Parry1, Bronwyn Myers2, Jonathan Caulkins3. 1. Alcohol, Tobacco and Other Drug Research Unit, South African Medical Research Council, Tygerberg 7505, South Africa; Department of Psychiatry, Stellenbosch University, Stellenbosch, Western Cape, South Africa. Electronic address: cparry@mrc.ac.za. 2. Alcohol, Tobacco and Other Drug Research Unit, South African Medical Research Council, Tygerberg 7505, South Africa; Department of Psychiatry and Mental Health, University of Cape Town, Western Cape, South Africa. 3. Heinz College, Carnegie Mellon University, Pittsburgh, PA, USA.