[1] Finnish Inst Occupat Hlth, Helsinki, Finland
[2] London Sch Hyg & Trop Med, Dept Social & Environm Hlth Res, London WC1, England
[3] UCL, Sch Med, Dept Epidemiol & Publ Hlth, London W1N 8AA, England
[4] Natl Inst Hlth & Welf, Dept Hlth Funct Capac & Welf, Helsinki, Finland
[5] Univ Turku, Dept Publ Hlth, SF-20500 Turku, Finland
[6] Harvard Univ, Sch Publ Hlth, Dept Soc Human Dev & Hlth, Boston, MA 02115 USA
[7] Turku Univ Hosp, FIN-20520 Turku, Finland