1. a Cancer Research UK Centre for Epidemiology, Mathematics and Statistics , Wolfson Institute of Preventive Medicine , London, UK
2. b Institute of Public Health, University of Copenhagen , Denmark
3. c Department of Mammography , Falun Central Hospital , Falun, Sweden
4. d Breast Test Wales , Cardiff, UK
5. e Icelandic Cancer Registry, Skógarhlíð , Reykjavík, Iceland