Advances in Life Course Research 47 (2021) 100359 Available online 21 July 2020 1040-2608/© 2020 Elsevier Ltd. All rights reserved. Sibling infuence on family formation: A study of social interaction effects on fertility, marriage, and divorce Zafer Buyukkececi *, Thomas Leopold University of Cologne, Albertus-Magnus-Platz, 50923, Cologne, Germany A R T I C L E INFO Keywords: Family formation Fertility Marriage Divorce Siblings Social interaction ABSTRACT This study examined social interaction effects on family formation and dissolution, asking whether fertility, marital, and divorce behavior spread in the sibling network. Using panel data from the German SOEP (1984 – 2016; N = 4,521 individuals), we estimated discrete-time event history models with random effects at the in- dividual to examine whether siblings’ transitions to parenthood, marriage, and divorce infuence an individual’s chance to have children, marry, and divorce. Results show that the hazard of becoming a parent increased in the short term after a sibling had a child. Similarly, the hazard of getting married increased following a sibling’s marriage. Tentative evidence also suggested that transition rates to divorce increased in the longer term following a sibling’s divorce. Furthermore, we found evidence for social interaction effects across different transitions in the process of family formation, as the transition rates to marriage decreased after a sibling divorced. Conversely, the risk of divorce decreased following a sibling’s entry to marriage. Overall, these fndings illustrate that the impact of network partners on demographic behavior is not limited to the same behavioral domain and might be negative as well as positive. 1. Introduction The life-course perspective emphasizes the importance of structural and social contexts for human development (Elder & Rockwell, 1979). The view is supported by demographic research showing that the occurrence and timing of life-course transitions such as fertility (Bon- gaarts & Watkins, 1996; Montgomery & Casterline, 1996) are infuenced not only by individual characteristics but also by the behavior of network partners. Recent research has directed attention to micro-level networks such as siblings (de Vuijst, Poortman, Das, & van Gaalen, 2017; Kotte & Ludwig, 2011; Lyngstad & Prskawetz, 2010), friends (Balbo & Barban, 2014), and colleagues (Asphjell, Hensvik, & Nilsson, 2013; Buyukkececi, Leopold, van Gaalen, & Engelhardt, 2020; Pink, Leopold, & Engelhardt, 2014) to examine social interaction effects on demographic behavior. These studies on social interaction effects and demographic behavior have focused on similar behavioral domains and argued why the same type of behavior may spread among network partners. Most of these studies have found positive associations between network partners’ demographic behavior, including fertility (e.g., Buyukkececi et al., 2020; Lyngstad & Prskawetz, 2010) and divorce (de Vuijst et al., 2017). Yet, two important aspects have been neglected in the literature. First, the infuence of network partners is not necessarily limited to the same behavioral domain. For instance, an individual’s entry into mar- riage may not only be infuenced by network partners’ marital behavior, but also by related behavior. Individual intentions underlying entries into parenthood and marriage tend to be similar, and attitudes towards these life-course transitions reinforce each other (Baiz´ an, Aassve, & Billari, 2003; Cowan & Cowan, 2000). Moreover, marriage is a precursor to parenthood and fertility decisions commonly take place in a context of marriage or cohabitation (Rindfuss, Morgan, & Swicegood, 1988), suggesting that not only network partners’ marital behavior but also their fertility behavior may have consequences for marital decisions. Second, network partners’ behavior may not only encourage but also discourage certain demographic behaviors. Extant studies commonly test for positive infuence, whereby network partners’ demographic transi- tions increase the chance of experiencing the same transition (Balbo & Barban, 2014; Lyngstad & Prskawetz, 2010). Network partners’ behavior, however, may also exert a negative infuence (Yakusheva & Fletcher, 2015). If network partners divorce, for example, this experi- ence may decrease the likelihood of marriage. In the present study, we aim to fll these gaps in the literature on * Corresponding author. E-mail addresses: zafer.bueyuekkececi@uni-koeln.de (Z. Buyukkececi), t.leopold@wiso.uni-koeln.de (T. Leopold). Contents lists available at ScienceDirect Advances in Life Course Research journal homepage: www.elsevier.com/locate/alcr https://doi.org/10.1016/j.alcr.2020.100359 Received 16 November 2019; Received in revised form 10 July 2020; Accepted 10 July 2020