Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Human Development and Family Studies

Committee Chair(s)

Shawn D. Whiteman


Shawn D. Whiteman


Diana Meter


Travis Dorsch


Aryn Dotterer


Sarfaraz Serang


As the longest lasting close relationship, often extending from birth until death, sibling relationships play an important role throughout the life course. To date, however, only limited work has examined the process by which siblings influence each other during young adulthood. Given that developmental differences between older and younger siblings diminish in young adulthood, it is possible that bidirectional (older-to-younger as well as younger-to-older) are more likely as compared to adolescence (in which top-down or older-to-younger influence has primarily been explored). It is further possible that processes of observational learning, including modeling, and sibling differentiation continue into young adulthood, shaping sibling similarities and differences as well as young adults’ overall well-being.

This three-study dissertation addressed these possibilities using extant data from three different studies. First, Study 1 examined the potential for bidirectional sibling influence on young adults’ binge drinking, marijuana use, risky sexual behaviors, and volunteering behaviors. Further, this study examined the degree to which sibling closeness exacerbated sibling similarities across these various domains. Next, Study 2 examined whether sibling relationship qualities (i.e., intimacy and conflict) mediated the longitudinal association between sibling differentiation and young adults’ well-being. Finally, Study 3 simultaneously examined whether and how domain specific sibling modeling and differentiation shaped sibling similarities and differences in young adults’ educational attainment, work prestige, and romantic relationship qualities.

Across the three studies, findings suggested that through different processes, siblings continue to influence each other during young adulthood. Overall, evidence for bidirectional sibling influence emerged in domains in which development was ongoing for both older and younger siblings during young adulthood (e.g., risky sexual behaviors, romantic relationships); however, evidence for top-down (or older-to-younger) socialization was more persistent across risky behavior domains. Across Studies 1 and 3, results did not support hypotheses that sibling modeling would promote greater similarities between young adult siblings. Study 2, in contrast, provided evidence that sibling differentiation longitudinally and indirectly shaped young adults’ well-being through their sibling relationship qualities, albeit in a direction inconsistent with theoretical propositions. Discussion focuses on the themes found across the studies and outlines future directions for research with siblings during young adulthood.