Siblings of children and adults with intellectual and developmental disabilities: psychological outcomes and sibling relationships

Siblings of children and adults with intellectual and developmental disabilities (IDD) have been the focus of research attention for several decades. This PhD thesis sought to build on that knowledge base, and included data about over 1,000 siblings of adults and children with IDD. This thesis has been able to draw upon large scale survey data to further understand siblings’ psychological outcomes as well as exploring areas less frequently considered in the sibling literature, including siblings’ school experiences and sibling relationships. Chapter one consisted of three main sections: a discussion about conceptual and theoretical perspectives about families, an overview of relevant, methodologically robust empirical literature, and a self-reflexive section that explored my experiences as a sibling. These three sections each highlighted methodological issues related to existing sibling research. Chapter two used representative, population-level data from the Millennium Cohort Study to examine the behavioural and emotional outcomes of older siblings of children with ID (n = 257) in comparison to older siblings of children without ID (n = 7246). Chapter three reported on an initial evaluation of a school-based intervention (Sibs Talk) for siblings (N = 55). Chapter four provided findings from the Adult Sibling Survey, these data constitute the largest UK sample of adult siblings of people with IDD (N = 911). This chapter examined adult siblings’ mental distress, wellbeing, quality of life, and health outcomes, using moderated multiple regression analyses. Chapter five presented sibling data from the 1,000 Families study. This study drew upon structural equation modelling to examine reciprocal effects about sibling relationship outcomes by considering the behavioural and emotional outcomes of both siblings (N = 500 sibling dyads). Chapter six synthesised the main contributions of these four empirical chapters, including a discussion about methodological limitations, as well as research, practice, and theoretical implications. Cumulatively, the research reported in this thesis showed that child and adult siblings had poorer psychological outcomes in comparison to other samples, but these poorer outcomes were likely related to contextual factors, such as socio-economic status and caring roles. Sibling dyad level analyses supported conceptualisations of reciprocity in the family system, with both children’s behaviour associated with sibling relationship quality. Sibs Talk was associated with promising positive outcomes. Notably, a simple negative narrative about the effect that people with IDD have on their non-disabled siblings was not supported by the evidence in this thesis