[1] Univ Ghent, Dept Publ Hlth, Unit Hlth Promot, B-9000 Ghent, Belgium
[2] Radboud Univ Nijmegen, Inst Behav Sci, NL-6500 HE Nijmegen, Netherlands
[3] Addict Switzerland, Res Inst, CH-1001 Lausanne, Switzerland
[4] Maastricht Univ, Sch Publ Hlth & Primary Care CAPHRI, Dept Hlth Promot, NL-6200 MD Maastricht, Netherlands