Research has indicated that fertility spreads through social networks and attributed this phenomenon to social interaction effects. It remains unclear, however, whether the findings of previous studies reflect the direct influence of network partners or contextual and selection factors, such as shared environment and common background characteristics. The present study uses instrumental variables to improve the identification of social interaction effects on fertility. Using data from the System of social statistical data sets (SSD) of Statistics Netherlands, we identify two networks—the network of colleagues at the workplace and the network of siblings in the family—to examine the influence of network partners on individual fertility decisions. Discrete-time event-history models with random effects provide evidence for social interaction effects, showing that colleagues’ and siblings’ fertility have direct consequences for an individual’s fertility. Moreover, colleague effects are concentrated in female-female interactions, and women are more strongly influenced by their siblings, regardless of siblings’ gender. These results are the first to demonstrate spillover effects across network boundaries, suggesting that fertility effects accumulate through social ties not only within but also across different domains of interaction.
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In this study, the term social interaction effects refers to the direct influence of network partners on an individual.
Ciliberto et al. (2016) used a dummy variable indicating whether any colleague’s sibling had a baby within the last two years and examined the impact of this variable on total number of children that women in a workplace had. Because this instrument should first influence the colleague’s fertility and then the focal person’s fertility through the colleague, it is likely that the effects are not captured within a two-year period.
Extending the risk period to more than one year would increase the risk of unidentified workers who left the workplace before September. Our restrictions ensured that people identified as colleagues were working at the firm in a given period.
Using a colleague’s sibling’s fertility as an instrument restricted the sample to only colleagues with siblings, who account for 87.5% of our target group. Accordingly, we additionally checked whether the fertility intentions of the excluded group differed from the individuals with siblings. Analyses using the Netherlands Kinship Panel Study (NKPS; Dykstra et al. 2012) showed that the intention to have a child—regardless of having a child or not—did not differ significantly between singletons and individuals with siblings in our study cohort. The only significant difference observed was that the desire to have three children was higher for individuals with two or three siblings compared with singletons.
We alternatively relaxed the matching criteria by excluding mother’s age at first birth and using a three-category measure of parental income to increase the number of matches. The findings are very similar to those presented in Fig. 4.
The findings are robust to increasing the threshold to 10,000 and 15,000 respectively.
We were not able to replicate these analyses for colleague effects because of colleagues with siblings living distant and also colleagues with siblings living close present within the same firm.
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This study was supported by the German Research Foundation (Grant Number EN 424/10-1) and the NORFACE DIAL project EQUALLIVES.
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Buyukkececi, Z., Leopold, T., van Gaalen, R. et al. Family, Firms, and Fertility: A Study of Social Interaction Effects. Demography 57, 243–266 (2020). https://doi.org/10.1007/s13524-019-00841-y
- Social interaction effects
- Social multipliers