In 1971, the Dutch-language branch of the Population and Family Study Centre (CBGS)* of the Department of Public Health and the Family organized, in collaboration with investigators from the Rijksuniversiteit Gent, the Katholieke Universiteit Leuven, and the Vrije Universiteit Brussels, the Second National Fertility Survey in Belgium (NEGO 11)** (Cliquet et al. , 1970). NEGO II was a result of and related to the First National Fertility Survey performed in Belgium (NEGO I) in 1966 (Cliquet, 1967; Morsa, 1967). Both of these surveys were modelled on the Growth of American Families (GAF)...