1. Cancer Epidemiology and Health Services Research Group, Centre for Public HealthQueen's University Belfast Belfast Northern Ireland United Kingdom
2. Centre for Cancer Research and Cell BiologyQueen's University Belfast Belfast Northern Ireland United Kingdom
3. Academic Primary Care, Institute of Applied Health SciencesUniversity of Aberdeen Aberdeen United Kingdom
4. Medical Statistics Team, Institute of Applied Health SciencesUniversity of Aberdeen Aberdeen United Kingdom
5. Section of Epidemiology and Population SciencesDepartment of Medicine, Baylor College of Medicine Houston TX
6. Dan L Duncan Comprehensive Cancer CenterBaylor College of Medicine Houston TX