[1] Uppsala Univ, Vastmanland Cty Hosp, Ctr Clin Res, Vasteras, Sweden
[2] Uppsala Univ, Dept Med Sci Resp Allergy & Sleep Res, Uppsala, Sweden
[3] Uppsala Univ, Dept Publ Hlth & Caring Sci, Family Med & Prevent Med, Uppsala, Sweden
[4] Orebro Univ, Fac Med & Hlth, Dept Resp Med, Orebro, Sweden
[5] Uppsala Univ, Dept Med Sci Occupat & Environm Med, Uppsala, Sweden
[6] Karolinska Inst, Sect Family Med & Primary Care, NVS, Stockholm, Sweden
[7] Acad Primary Care Ctr, Stockholm, Sweden
[8] Karolinska Inst, Dept Med, Clin Epidemiol Div, Stockholm, Sweden
[9] Ctr Clin Res & Educ, Sodertalje, Sweden
[10] Orebro Univ, Sch Med Sci, Fac Med & Hlth, Orebro, Sweden
[11] Orebro Univ, Sch Med Sci, Fac Med & Hlth, Clin Epidemiol & Biostat, Orebro, Sweden
[12] Univ London Univ Coll, Dept Epidemiol & Publ Hlth, London, England
[13] Uppsala Univ, Dept Med Sci, S-75185 Uppsala, Sweden