[1] Northumbria Univ, Fac Engn & Environm, Dept Math Phys & Elect Engn, Newcastle Upon Tyne, Tyne & Wear, England
[2] Univ Witwatersrand, Sch Publ Hlth, Div Epidemiol & Biostat, Johannesburg, South Africa
[3] British Assoc Dermatologists, Willan House,Fitzroy Sq, London, England
[4] Univ Warwick, Warwick Med Sch, Warwick Ctr Appl Hlth Res & Delivery, Coventry, W Midlands, England