Department of Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, PO Box 85500, 3508 GA, Utrecht, the Netherlands. Epidemiology Program, Division of Public Health Sciences, Fred Hutchinson Cancer Research Centre, Seattle, Washington, USA. Department of Epidemiology, School of Public Health, and Department of Medicine, School of Medicine, University of Washington, Seattle, Washington, USA. Cochrane Netherlands, University Medical Center Utrecht, Utrecht, the Netherlands. MRC-PHE Centre for Environment and Health, Department of Epidemiology and Biostatistics, School of Public Health, Imperial College, London, UK. Department of Cancer Epidemiology and Prevention Research, CancerControl Alberta, Alberta Health Services, Alberta, Canada. Department of Oncology, Cumming School of Medicine, University of Calgary, Calgary, Canada. Department of Community Health Sciences, Cumming School of Medicine, University of Calgary, Calgary, Canada. Department of Epidemiology, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, PO Box 85500, 3508 GA, Utrecht, the Netherlands. E.Monninkhof@umcutrecht.nl.