Background: Policy guidelines recommend service user involvement in care and treatment decision-making as a person-centred approach to improving health outcomes. However, most shared decision-making (SDM) models are perceived as a rational process. There is a need for research exploring the role of emotions in children and young people’s mental health (CYPMH) decisions. This thesis aimed to develop an affective appraisal approach to SDM based on theory and evidence and to develop and pilot an intervention to support parents/carers and promote SDM. Methods: Several study designs were adopted. (1) Qualitative synthesis to understand the emotional experiences of parents. (2) Logistic regression analysis of parental help-seeking. (3) Multilevel modelling to investigate SDM in CYPMH services. (4) Interviews and focus groups with parents/carers and healthcare professionals to further explore the effect of emotions on SDM. (5) Scoping review to identify and examine existing decision support interventions. (6) Feasibility and acceptability randomised controlled trial of a novel intervention. Findings: (1) Seven categories describing parents’ emotions emerged as influencing factors to CYPMH care and treatment decisions. (2) A negative association between parental worry and help-seeking was found. (3) Almost 70% of parents reported experiencing SDM in CYPMH, and findings justified a multilevel approach to studying SDM. (4) A framework for an affective appraisal model of SDM emerged. (5) Twenty-three existing interventions were identified, incorporating an average of 4.57 elements of SDM. Time, accessibility and appropriateness emerged as factors influencing usage and implementation. (6) Although, the novel intervention (Power Up for Parents) was found to be acceptable, some changes to the recruitment strategy may be needed before upgrading to a full trial. Conclusion: This thesis provides a theoretical understanding that parents are ‘expected to, but not always able to’ be actively involved in care and treatment decisions. Integrating this concept in CYPMH may help to inform policy and practice for the implementation of SDM. These findings also provide insight for researchers to establish a foundation for developing future interventions using the affective appraisal approach
