Can Spatial Diffusion Process Explain Family Changes? A Spatio-Temporal Analysis of Nonmarital Births Over 50 Years in Belgium (1968–2017)

Abstract

Over the decades, many European countries have experienced significant changes in the family, characterised by declining marriage rates, increasing cohabitation, delayed childbearing and persistently low fertility. The Second Demographic Transition (SDT) has been a key framework for understanding these shifts, with alternative theories focusing on economic, cultural, and gender-related factors. Despite extensive research, the geographical dimension of these changes remains underexplored, in particular a detailed spatio-temporal analysis of the determinants of their spatial dynamics from their onset. This study fills this gap by examining the spatial dynamics of nonmarital births in Belgium over the last 50 years at the municipal level and by tracing the evolution of key explanatory variables. Using spatial modelling, we find a significant spatial diffusion effect, i.e. that nonmarital birth rates in a municipality are influenced by rates in neighbouring municipalities from previous periods. This finding highlights the importance of geographical proximity as a key determinant of family change, alongside socioeconomic factors. In addition, the study identifies the factors driving these spatial dynamics, quantifies their relative impact, and systematically ranks them across time. It suggests that different theoretical frameworks are relevant to explain the different stages of the diffusion process. Our findings emphasize the need to integrate multiple theoretical perspectives to achieve a comprehensive understanding of the family changes.