The more, the merrier? Young adults’ sibling relationship quality in medium to large families

Approximately 80% of individuals from the United States have at least one sibling. Of those with siblings, a little more than half have two or more siblings. Yet, research on siblings across the life course, including young adulthood, has focused primarily on sibling dyads rather than larger sibling groups or multiple sibling dyads from the same family. The overarching aim of the current study was to explore the form and impacts of entire sibling groups and multiple sibling dyads for young adults with two or more siblings. Data were collected from an online survey of 975 young adults aged 19–29 years from across the United States ( M age = 25.43, SD = 2.52; 48% male; 73% white). Results showed that participants reported greater variation in sibling relationship quality when their siblings were not all the same gender and when their siblings had greater differences in age. Young adults were more likely to report a close aged sibling as the sibling with whom they have the closest relationship or most conflict. Relationship quality also showed links with psychosocial outcomes. In some cases, greater variation in sibling conflict and closer relationships with one particular sibling were linked to better outcomes. More conflict was linked to poorer outcomes. Multiple effects were moderated by gender, gender of the sibling, and characteristics of the entire sibling subsystem. Overall, our findings suggest that sibling relationships in medium to larger families are multifaceted and complex. Our results are in line with a family systems perspective that siblings have unique roles but that sibling dyads within families mutually influence and interact with one another.