Demographic challenges for the 21st century : a state of the art in demography : conference organized as a tribute to the continuing endeavours of Prof. Dr. Em. Ron Lesthaeghe in the field of demography - Surkyn, J.; Deboosere, Patrick.; Bavel, Jan Van.; Willekens, Frans.; Koloriet, Sterrebeek. (VUBPress, 2008)