Sibling Complexity and Mental Health Outcomes in Late Adolescence – Evidence from Finnish Birth Cohorts

Liina Junna , University of Helsinki
Lauren Bishop, University of Helsinki
Hanna Remes, University of Helsinki
Pekka Martikainen, University of Helsinki

Family complexity and instability related to parental unions have been linked to children’s mental ill-health. Emerging research also suggests that the presence of half- and stepsiblings may further influence mental health, yet disentangling sibling complexity from parental union dynamics from remains empirically challenging. This study examines how the family type (e.g., residing with two biological parents throughout childhood, one reconstituted family) with and without half- and stepsiblings is associated with adolescent outcomes. Using Finnish administrative register data, we follow all children born between 1998–2002 (n ˜ 280,000). We identify biological parents, their cohabiting partners, and all full, half-, and stepsiblings of the index child from birth to age 16. Regression models are used to assess associations between sibling complexity and psychiatric disorders and self-harm between ages 17–19, based on specialized care and mortality records. Propensity score matching on parental union history prior to the birth of the index child and socioeconomic status creates comparable groups with and without sibling complexity. Preliminary findings suggest that, regardless of family type, adolescents with half- or stepsiblings face elevated risks of psychiatric outcomes. For instance, in crude models, children growing up with two biological parents along with older half-siblings had a 29.0% (95% confidence interval 17.3-41.7) higher risk of psychiatric disorders compared to children in two biological parent families without sibling complexity. This study uniquely captures both parental unions and siblings across childhood among full birth cohorts, offering new insights into how family complexity shapes adolescent health and wellbeing.

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 Presented in Session P6. Health, Mortality, and Ageing 2