Heinrich, Martina Isabel.
Sibling relationships have a great impact on children's social and psychological development. This thesis provides an all-encompassing examination of the precursors and outcomes of sibling bullying through three quantitative studies: the first study, a meta-analysis, provides a foundational schema of the factors associated with sibling conflicts; the second study, a short-term longitudinal study, examines the individual and proximal precursors of sibling bullying and its short-term outcomes (one and two years later); the third study, a long-term longitudinal study, examines the distal precursors of sibling bullying and its long-term outcomes (five years later). The first study assessed the strongest effect sizes associated with sibling conflicts. It examined the link between parent-child relationships, familial factors and sibling conflicts. Studies were identified through a systematic search, coded, and selected based on criteria relevant for this study resulting in 60 studies (178 effect sizes), which in total involved 43,270 participating children and adolescents. Studies were categorised as proximal and distal factors. Those involved in sibling conflicts were significantly less likely to have authoritative, and warm and affectionate parents, and less likely to come from families with affluent socioeconomic-status, positive family climate and good marital quality. Conversely, more sibling conflicts were significantly related to abusive and neglectful parents, and parent-child conflicts; and more likely to come from families with poor mental health, low SES, adverse family atmosphere and parental conflict. The factors were moderated by assessment methods, study design, direction and form conflict, gender constellation, and continent. This study served as a building block for the two following studies, as it highlighted key factors to focus on in further assessing the precursors and outcomes of sibling bullying. The second study, which was based on the Edinburgh Study of Youth Transition and Crime (ESYTC, 2014) found that parenting factors were crucial to sibling bullying. Parental involvement, parent-child conflict and parent-child leisure time were precursors and outcomes of sibling bullying, so that more parental involvement and parent-child leisure time were associated with less sibling bullying perpetration and victimisation. Further, sibling bullying perpetration and sibling victimisation were precursors of peer bullying perpetration and victimisation one and two years later. However, the strength of the association declined over the course of two years. Impulsive behaviour and social alienation seem to be fundamental influencing factors in the development of sibling bullying and sibling victimisation, respectively. Additionally, children who were involved in peer bullying were more likely to have been involved in sibling bullying, compared to peer neutrals one and two years later. The third study, which was based on the Avon Longitudinal Study of Parents and Children (ALSPAC, Boyd et al., 2012) found that maternal somaticism was the strongest predictor of sibling bullying. Further, the strongest predictor of sibling victimisation was partner-to-mother verbal violence. Symptoms of depression at 16.5 years of age was the strongest outcome of sibling bullying perpetration and victimisation at 12.5 years of age. Children who were peer bully-victims when they were 17.5 years old were more likely to have been sibling pure bullies and sibling bully-victims, compared to children who were peer neutrals. The results suggest that familial factors significantly influence the quality of sibling relationships. Additionally, the findings show that sibling bullying is related to peer bullying, so that children mirror bullying behaviours across social contexts (i.e. family environment and school environment). The findings of this thesis are important for clinical practitioners, social workers, parents and schools. Based on these findings practitioners could tailor family and parenting intervention programs that prevent siblings from establishing conflictual relationships with one another. Particularly, it is suggested that bullying intervention programs should integrate three aspects: family members should play an integrated and active role in their plans to reduce bullying and victimisation; bullying intervention and prevention studies should commence at preschool ages; positive family climate should actively be nurtured, in addition to lowering hostility.