@article{De Graaf2009,
author = {De Graaf, H. and Vanwesenbeeck, I. and Meijer, S. and Woertman, L. and Meeus, W.},
title= {Sexual trajectories during adolescence: Relation to demographic characteristics and sexual risk},
year = {2009},
doi = {10.1007/s10508-007-9281-1},
volume = {38},
pages = {276--282},
}