[1] Univ Newcastle Upon Tyne, Ctr Hlth Serv Res, Newcastle Upon Tyne NE2 4AA, Tyne & Wear, England
[2] Ottawa Hlth Res Inst, Clin Epidemiol Programme, Ottawa, ON, Canada
[3] Univ Aberdeen, Sch Med, Hlth Serv Res Unit, Aberdeen AB25 2ZD, Scotland
[4] Univ Aberdeen, Sch Psychol, Aberdeen AB24 2UB, Grampian, Scotland
[5] Univ Dundee, Sch Dent, Dental Hlth Serv Res Unit, Dundee DD1 4HR, Scotland