Fertility and Well-Being


Decoding the Rollercoaster Fertility Age

Sebastian Klüsener, Robert Stelter; in Collaboration with Sandra B. Krapf (University of Cologne, Germany), Nora E. Sánchez Gassen (Nordregio, Stockholm, Sweden)

Detailed description:

Since the onset of the demographic transition in the 19thcentury, fertility trends in advanced-developed countries have been the focus of a large number of studies. The observed period trend patterns frequently resemble a rollercoaster. However, despite extensive research efforts, some aspects of these patterns remain rather poorly understood. This includes the factors behind the baby boom in the mid-20th century and fertility trajectories often seeming to stay quite stable over longer periods of time: In many countries, the major fertility trends over the last 150 years can be divided into a small number of longer phases in which fertility was either falling, rising, or rather stable. Theoretical explanations for specific trends are frequently developed ex-post in a quite deterministic manner pointing to specific driving factors. A drawback of such accounts is that they usually offer limited guidance for anticipating future fertility trajectories especially when there is a high degree of uncertainty about the potential driving factors. In addition, most theoretical explanations focus on specific sub-periods (such as the fertility decline during the demographic transition, the baby boom, or the changes after 1960), and few attempts have been made to develop a unifying framework that allows to explain all of the major fertility trends over the last 100 to 150 years.

This project aims to develop such a unifying framework by identifying the key determinants and mechanisms that may have contributed to the major fertility trends experienced by specific advanced-developed countries since the onset of the demographic transition. Key determinants relate to aspects such as the transition from an agricultural to an industrial society, and later on to a service society. They also include gender issues and welfare state contexts. Mechanisms, by contrast, are concerned with how shifts in fertility behavior are unfolding in societies. Here, we are interested in how the emergence of mismatches between social and economic practices and social and economic regulatory frameworks (such as policies) might cause disturbances in fertility trends. We also explore whether fertility trends are stabilized by momentum effects due to social interactions, where birth events or their absence might affect future birth decisions of other persons.

We are testing the theoretical framework developed in this project with agent-based simulation models. Our aim is to simulate the major fertility trends for a selected number of countries since the onset of the demographic transition. We have chosen to focus first on Sweden and Spain. Our models simulate large cohorts progressing through childbearing ages while subject to social and economic changes in, for example, sectoral employment and educational expansion. These changes affect the life courses of the simulated agents and their family formation decisions. Based on these models, we will explore whether our theoretical explanations allow us to replicate the fertility trajectories experienced by the studied countries since the onset of the demographic transition. If these simulations are successful, we might be able to also use them to better predict future fertility trajectories.

Research keywords: Fertility Development

Region keywords: Germany; Spain; Sweden; USA