[1] Univ Manchester, Sch Dent, Manchester, Lancs, England
[2] Univ Strathclyde, Sch Psychol Sci & Hlth, Glasgow, Lanark, Scotland
[3] Univ Liverpool, Dept Biostat, Liverpool, Merseyside, England
[4] Salford Royal NHS Fdn Trust, Salford, Lancs, England
[5] Univ Salford, Sch Hlth Sci, Salford, Lancs, England
[6] Queen Mary Univ London, Barts & London Sch Med & Dent, London, England