If a child is born to a sibling or a colleague, this can trigger a chain reaction. This is the key finding of a study that ISS researchers Zafer Büyükkeçeci and Thomas Leopold recently published in cooperation with colleagues from The Hague and Bamberg.

The authors analyzed data from the Dutch System of Social Statistical Datasets (SSD), in which various registers are linked. This data source contains information on family members and the workplace, allowing the researchers to link these two networks.

The results show that if a colleague becomes a mother, the chance of a pregnancy increases. The same effect can be found between siblings: After the birth of nieces and nephews, the chance of a pregnancy increases. In addition, the study is the first to demonstrate so-called spillover effects across network boundaries: If persons are infected with the desire to have a child, they in turn influence their siblings - and these in turn influence their own colleagues. Conversely, people in reproductive age who rarely experience births in among their siblings and colleagues are less likely to have children.

The study could not examine in detail which mechanisms are responsible for the contagiousness of having babies. If a child was born to a sibling or a colleague, however, then this was more contagious for women than for men. The researchers suggest that this kind of contagion effect at the workplace is primarily due to social learning: A woman who successfully reconciles work and family life is a role model to her colleagues. In the contagion between siblings, the emotional closeness to newborn nieces and nephews may also play a role. The study could not offer definitive conclusions about the overall importance of contagion effects. However, a simulation showed that without contagion effects, the number of births would have been around 5% lower in the study period.