1. Department of Community Medicine, Institute of Public Health, University of Cambridge Forvie Site, Robinson Way, Cambridge CB2 2SR, United Kingdom
2. Public Health Resource Unit, Institute of Public Health, University of Cambridge Forvie Site, Robinson Way, Cambridge CB2 2SR, United Kingdom
3. Cambridge and Huntingdon Breast Screening Service, Rosie Maternity Hospital, Robinson Way, Cambridge CB2 2SW, United Kingdom
4. Norwich Breast Screening Unit, Norfolk and Norwich Hospital, Brunswick Road, Norwich NR1 3SR, United Kingdom
5. MRC Biostatistics Unit, Institute of Public Health, University of Cambridge Forvie Site, Robinson Way, Cambridge CB2 2SR, United Kingdom