1 Department of Epidemiology Research, Division of National Health Surveillance and Research, Statens Serum Institut, DK-2300 Copenhagen S, Denmark and Department of Clinical Medicine, Center for Sexology Research, Aalborg University, DK-9000 Aalborg, Denmark MFR@ssi.dk.
2 Department of Epidemiology Research, Division of National Health Surveillance and Research, Statens Serum Institut, DK-2300 Copenhagen S, Denmark.