[1] UCL, Dept Epidemiol & Publ Hlth, London WC1E 6BT, England
[2] MRC, Social & Publ Hlth Sci Unit, Glasgow, Lanark, Scotland
[3] Univ Sydney, George Inst Int Hlth, Sydney, NSW 2006, Australia
[4] Univ Bristol, Dept Social Med, Bristol, Avon, England
[5] Univ Oxford, Clin Trial Serv Unit, Oxford, England
[6] Univ Oxford, Epidemiol Studies Unit, Oxford, England
[7] Finnish Inst Occupat Hlth, Helsinki, Finland