1 Institute of Medical Epidemiology, Biostatistics and Informatics and Department of Gynaecology, Martin Luther University Halle-Wittenberg, 06097 Halle (Saale), Germany. Electronic address: Eva.kantelhardt@uk-halle.de.
2 Institute of Medical Epidemiology, Biostatistics and Informatics and Department of Gynaecology, Martin Luther University Halle-Wittenberg, 06097 Halle (Saale), Germany.