Department of Public Health and Primary Care, Strangeways Research Laboratory, University of Cambridge, 2 Worts Causeway, Cambridge, CB1 8RN, UK. ap736@medschl.cam.ac.uk.|Department of Public Health and Primary Care, Strangeways Research Laboratory, University of Cambridge, 2 Worts Causeway, Cambridge, CB1 8RN, UK. amw79@medschl.cam.ac.uk.|Department of Public Health and Primary Care, Strangeways Research Laboratory, University of Cambridge, 2 Worts Causeway, Cambridge, CB1 8RN, UK. mjl81@medschl.cam.ac.uk.|Department of Oncology, Strangeways Research Laboratory, University of Cambridge, 2 Worts Causeway, Cambridge, CB1 8RN, UK. jpt34@medschl.cam.ac.uk.|Department of Public Health and Primary Care, Strangeways Research Laboratory, University of Cambridge, 2 Worts Causeway, Cambridge, CB1 8RN, UK. pp10001@medschl.cam.ac.uk.