[1] Univ Surrey, Fac Med & Hlth Sci, Sch Hlth Sci, Guildford GU2 7YH, England
[2] Univ Surrey, Fac Arts & Social Sci, Sch Sociol, Guildford GU2 7XH, England
[3] Northern Care Alliance NHS Fdn Trust, Mayo Bldg,Salford Royal,Stott Lane, Salford M6 8HD, England
[4] Kings Coll London, Fac Life Sci & Med, Dept Populat Hlth Sci, Guys Campus, London SE1 1UL, England