1. Centre for Reproductive Medicine, Amsterdam UMC, Academic Medical Centre, Meibergdreef 9, Amsterdam, the Netherlands
2. Department of Biostatistics and Research Support, Julius Centre, University Medical Centre Utrecht, Heidelberglaan 100, Utrecht, the Netherlands
3. Medical Statistics Team, Institute of Applied Health Sciences, University of Aberdeen, Aberdeen, UK
4. Institute of Applied Health Sciences, University of Aberdeen, Aberdeen, UK
5. Medical Statistics, Department of Biomedical Sciences, Leiden University Medical Centre, Einthovenweg 20, Leiden, the Netherlands