Oh half brother, where art thou? The boundaries for full- and half sibling interaction

Background: Previous research indicates that both full and half siblingships have the potential to develop into enduring social relationships, providing that the siblings have the opportunity to interact with one another during childhood and adolescence.

Objective: This study estimates: (1) how much time half and full siblings may be exposed to each other during childhood and adolescence; (2) how half sibling exposure is conditional on birth spacing and residency; and (3) the extent to which parents’ social vulnerability is associated with different levels of lifetime exposure to half siblings.

Method: This study uses Swedish register data to calculate exposure to half siblings based on birth spacing and registered residency for all full and half siblings to the 1994 birth cohort.

Results: A substantive share of half siblings are less exposed each other due to lengthy birth spacing and residency patterns. By age 18, 26% of the birth cohort have had a half sibling also no older than 18 for at least one year. By age 18, 13% of the birth cohort have had a half sibling no older than 18 for up to 10 years. By age 18, 8% of the birth cohort was registered in the same dwelling as another half sibling for eight years or more. Parents’ social vulnerability does not predict exposure to half siblings among the population who has at least one half sibling by age 18.

Conclusion: Even though half siblings constitute a large share of all siblings, full siblings will likely make up the vast majority of the siblingship-like relationships because so many half siblings are unable to interact during childhood or adolescence due to extensive age differences and/or because they do not co-reside.

Contribution: This study quantifies the boundaries for exposure to full and half siblings across childhood and adolescence. It highlights the benefits of including a population perspective and a child’s perspective to full and half sibling social relationships.