Does Fertility Behavior Spread Among Friends?

In the past few years there has been a growing recognition of the effect of peers on an individual’s behaviour. Recent sociological literature has shown, for instance, that friends influence each other in areas such as smoking, drinking, and how much we exercise. In our recently published paper, we examine the influence of friends on an individual’s decision to have a child. So far, research on fertility behavior has largely neglected the fact that people are embedded in social networks, thereby failing to acknowledge that couples do not make fertility choices in a vacuum.

Whereas in the past, family ties and ascribed relationships could be considered the main source of social influence on an individual’s behavior, this is less true in today’s advanced societies. We now live in societies characterized by greater individualism and mobility of individuals; therefore networks of voluntary relationships, such as friendships, have become increasingly influential, perhaps even more influential than kinship networks. It is therefore interesting to consider whether and how friends can affect an individual’s fertility behavior.

We identify three main mechanisms by which friends might influence an individual’s decision to have a child. First, people compare themselves to their friends. Being surrounded by friends who are new parents makes people feel pressure to have children as well. Second, friends are an important learning source. Becoming a parent is a radical life change. By observing their friends, people learn how to fulfill this new role. Lastly, having children at the same time as friends may bring many advantages — friends can share the childbearing experience and thus reduce the stresses associated with pregnancy and childrearing. It is also easier for people to remain friends when they are experiencing parenthood at the same time.

We use data from the National Longitudinal Study of Adolescent to Adult Health (Add Health) on more than 1,700 American women who were tracked from when they were around 12/15-years-old through approximately age 30. We focus on dyads of friends who start their friendship during high school and remain friends also afterwards. Within each dyad, we examine whether a friend’s childbearing increases the propensity of the other friend to have her first child. Studying friendships that were formed at the age of 15 allows us to distinguish influence from selection. Friendships that are formed later in life, when the individual is already an adult, may be formed because of similarities in family plans and attitudes. This would mean that friends may have similar fertility behaviors because they have chosen themselves as similar and not because they have influenced each other. By looking at friendships that are formed in early adolescence we avoid this ambiguity. It is indeed unlikely that girls at that early stage in life choose their friends because they share similar family plans.

We show that the likelihood of a woman having a first child increases after a friend gives birth, reaches a peak approximately two years later, and then decreases (see graph below). The contagion is negligible in the long run. The fact that the effect is not immediate is likely because it takes time to have a child, because there is a natural period before conception and because the desire to have a child develops over time. It also makes sense that we do not find an effect in the long run, insofar as cost-sharing dynamics may not occur if the distance between the two friends’ childbearing experiences is large.

Overall, this research demonstrates that fertility decisions are not only influenced by individual characteristics and preferences, but also by the social network in which individuals are embedded. It is interesting that the contagion seems to occur only between intended pregnancies, meaning that friends influence each other predominantly when the fertility decision-making is rational and the choice deliberate.



This post has been jointly written by Nicoletta Balbo and Nicola Barban, Senior Research Associate, Department of Sociology, University of Oxford, UK.


Nicoletta Balbo & Nicola Barban, (2014), Does fertility behavior spread among friends? American Sociological Review, 79 (3), 412-431.

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Nicoletta Balbo

About Nicoletta Balbo

Nicoletta Balbo is a post-doctoral researcher at the Dondena Centre for Research on Social Dynamics and Public Policy/ Bocconi University in Milan, Italy. Nicoletta's research interests are in the field of family sociology and social demography, with a focus on fertility dynamics, social networks, subjective well-being and adolescent health.

2 thoughts on “Does Fertility Behavior Spread Among Friends?

  1. Childbearing and fertility control (contraception etc) patterns and changes are well-known to be propagated through social networks. There is a huge existing literature on this that you need to learn about. See the book by Hans-Peter Kohler on fertility as a “contagion” process–it was his dissertation several years ago.

  2. Hi Woody–great to hear from you! Indeed, in the ASR article Nicoletta and Nicola make ample reference to work by H-P Kohler (and earlier Montgomery-Casterline among others). I think the key contribution here is the emphasis on selectivity and on the timing of influence in the setting of ‘rich’ societies. There is certainly more to say than one could put in a blog entry (where unavoidably scientific references are hidden).
    Francesco B

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