1. Instituto Previdencia dos Servidores do Estado de Minas Gerais; Minas Gerais Brazil
2. University College London; Department of Epidemiology and Public Health; London UK
3. Leiden University Medical Center; Epidemiology; PO Box 9600 Leiden Netherlands 2300RC
4. Leiden University Medical Center; Department of Clinical Epidemiology; PO Box 9600 Leiden Netherlands 2300RC
5. Leiden University Medical Center; Department of Gynaecology, Division of Reproductive Medicine and Dept. of Clinical Epidemiology; PO Box 9600 Albinusdreef 2 Leiden Netherlands NL 2300 RC
6. Leiden University Medical Center; Department of Medical Statistics; PO Box 9600 Leiden Netherlands 2300 RC