Pamela L Cross1
, Deborah Ashby3
, Geoff Harding1
, Enid M Hennessy3
, Louise Letley2
, Suzanne Parsons1
, Anne E Spencer4
and Martin Underwood1
for the TOIB Study Team1,2,3,4 
1Centre for Health Sciences, Barts and The London, Queen Mary's School of Medicine and Dentistry, 2 Newark Street, Whitechapel, London E1 2AT, UK
2Medical Research Council General Practice Research Framework, Stephenson House, North Gower St, London NW1 2ND, UK
3Wolfson Institute of Preventive Medicine, Barts and The London, Charterhouse Square, London EC1M 6BQ, UK
4Department of Economics, Queen Mary's University of London, Mile End Road, London E1 4NS, UK