[1] Univ Aberdeen, Epidemiol Grp, Aberdeen, Scotland
[2] Univ Aberdeen, Med Stat Team, Aberdeen, Scotland
[3] Univ Manchester, Arthrit Res UK Epidemiol Unit, Manchester, Lancs, England
[4] Univ Aberdeen, Hlth Econ Res Unit, Aberdeen, Scotland
[5] Univ Manchester, Sch Nursing Midwifery & Social Work, Manchester, Lancs, England
[6] Univ Aberdeen, Aberdeen, Scotland
[7] Pennine Acute Hosp NHS Trust, Hlth Res Ctr, Manchester, Lancs, England