1. National Heart and Lung Institute, Imperial College London, London, United Kingdom
2. Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom
3. Medical Research Council Biostatistics Unit, University of Cambridge, Cambridge, United Kingdom
4. Department of Applied Economics, Erasmus School of Economics, Erasmus University Rotterdam, Rotterdam, the Netherlands
5. Erasmus University Rotterdam Institute for Behavior and Biology, Erasmus University Rotterdam, Rotterdam, the Netherlands
6. Department of Obstetrics and Gynaecology, Chelsea and Westminster National Health Service Trust, London, United Kingdom