Do family, friends or work colleagues influence each other’s fertility decisions? If so, to what extent does this generate a multiplying effect in societies? Previous studies have shown that the decision of having a child is associated with social networks people have. It suggests that mechanisms such as social learning and social pressure lead to a "contagious" effect inside social networks. However, this literature does not explain whether this spill over effect reflect a direct influence of network partners or is rather a reflection of contextual and selection factors, such as shared environment and common background characteristics.
In a new study published in Demography, Zafer Buyukkececi (Humboldt-Universität zu Berlin), Thomas Leopold (University of Amsterdam), Ruben van Gaalen (Statistics Netherlands) and Henriette Engelhardt (University of Bamberg) answered these questions with data from the System of social statistical data sets (SSD), an integrated longitudinal database of various registers and surveys provided by Statistics Netherlands. The database holds information on the entire Dutch population, and individuals can be linked to family members and colleagues through unique individual and workplace identifiers.
To identify the effects of colleagues and siblings on fertility, the authors used information about the fertility of colleagues’ siblings and siblings’ colleagues: As shown in Fig.1, this strategy connected both interaction domains that can operate only through direct colleague and sibling influences to the transition to parenthood. This made it possible to analyse direct colleague and sibling effects as well as possible spill over effects from the family to the workplace and vice versa.
Fig. 1 Identification of social interaction effects
Results indicate that colleagues’ and siblings’ fertility have direct consequences for an individual’s fertility, demonstrating, for the first time, a clear fertility social spill over effect from family to the workplace and vice versa.