Background: Emotion regulation involves managing which emotions we experience, when and how we feel them, and how we express them. Difficulties in emotion regulation, known as emotion dysregulation, are central to many mental health conditions. With significant overlap across psychiatric diagnoses, transdiagnostic approaches to understanding and treating these issues are gaining attention. Adolescence is marked by major physical, psychological, and social changes, alongside heightened emotional experiences and the onset of many psychiatric disorders. This highlights the importance of addressing emotion dysregulation in child and adolescent psychiatric care, and the need to evaluate its assessment and explore transdiagnostic interventions.

The overarching aim of this thesis was twofold: first, to examine the assessment of emotion dysregulation in adolescents within child and adolescent psychiatric services; and second, to evaluate the feasibility, outcomes and experiences of a brief adjunctive emotion regulation skills training.

In Study I, the psychometric properties of a brief version of the Difficulties in Emotion Regulation Scale (DERS-16; Bjureberg et al., 2016) were examined in a child and adolescent psychiatric sample (n = 281). The DERS-16 was also used to assess emotion dysregulation in a community sample (n = 3,169). A two-step cluster analysis was conducted to identify subgroups within the clinical sample. Study II was a pilot study evaluating a brief emotion regulation skills training group delivered jointly to adolescents (n = 20) and their parents (n = 21) in an outpatient child and adolescent psychiatric setting. The aim was to assess the feasibility and outcomes of the intervention using a within-group design. Pre- and post-assessments consisted of self-report measures and a written consumer satisfaction questionnaire. Study III was a randomised controlled study of a brief emotion regulation skills training group. A transdiagnostic sample of adolescents (n = 118) from two child and adolescent psychiatric clinics was randomised to either the intervention group or an active waitlist control. Data were analysed using intent-to-treat principles, with analysis of covariance and exploratory within-group analyses conducted. In Study IV, qualitative interviews were conducted with 10 adolescents and 11 parents regarding their experiences of participating in the emotion regulation skills training. Reflexive thematic analysis was used to analyse the interview data. The findings from Study I demonstrated that the DERS-16 showed acceptable psychometric properties within a child and adolescent psychiatric sample. The measure effectively distinguished between the clinical and community samples in terms of emotion dysregulation. The cluster analysis resulted in a three-cluster solution where the group with highest self-reported emotion dysregulation also were characterised by greater comorbidity, increased risk behaviours, and higher levels of exposure to abuse. Study II indicated that the brief emotion regulation skills training group was feasible, with 87% of participants completing the intervention. Participants generally reported increased knowledge of emotions. Participants showed significant reduction in emotion dysregulation, assessed with Difficulties in Emotion Regulation Scale (DERS; Gratz & Roemer, 2004) and in alexithymia. The results of Study III showed that participants in the brief emotion regulation skills training group experienced significant reductions in difficulties related to emotional clarity and symptoms of alexithymia compared to those in the control group. There were no significant differences in overall emotion dysregulation, or symptoms of depression and anxiety. In Study IV, qualitative analysis yielded three overarching themes: Parent–Child Processes, Individual Processes, and Group Processes. Participants identified improvements in the parent–child relationship as the primary outcome of the intervention.

The studies in this thesis showed that adolescents in psychiatric care reported greater difficulties with emotion dysregulation than those in the community. The DERS-16 proved suitable for assessing these difficulties, which were linked to higher comorbidity and risk behaviours. A brief emotion regulation skills training, delivered jointly to adolescents and parents, was feasible and associated with reduced difficulties in emotional clarity and symptoms of alexithymia in adolescents. Both adolescents and parents also reported improvements in their relationship following the training.