[1] Karolinska Inst, Dept Med, Clin Epidemiol Unit, Stockholm, Sweden
[2] Karolinska Univ Hosp, Karolinska Insitutet, Dept Med, Rheumatol Unit, Stockholm, Sweden
[3] Rheumatol AIR, Dept Clin & Expt Med, Linkoping, Sweden
[4] Stanford Sch Med, Hlth Res & Policy Dept, Div Epidemiol, Stanford, CA USA
[5] Stanford Sch Med, Dept Med, Div Rheumatol & Immunol, Stanford, CA USA
[6] Karolinska Inst, Dept Med, Clin Epidemiol Unit, Stockholm, Sweden