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Functioning, the ability to perform important tasks in life, varies greatly among psychiatric patients. Factors such as comorbidity, personality disorders, trauma, personality and attachment style have been linked to functioning, but never studied together. This thesis aims to explore functioning in psychiatric patients by validating clinical measurement tools and identifying key factors influencing it.

Paper I evaluated the psychometric properties of the Sheehan Disability Scale (SDS) in a sample of 160 young psychiatric patients diagnosed with ADHD, Bipolar Disorder, or Borderline Personality Disorder. Exploratory factor analysis confirmed a one-factor structure, and the SDS demonstrated high internal consistency and concurrent validity. The study supports the tool's reliability and utility in clinical settings for assessing functioning.

Paper II evaluated the psychometric properties of the Early Trauma Inventory (ETI) in 243 young psychiatric patients and 56 controls. The factor analysis confirmed the previously seen four-factor model, and showed good to acceptable fit. Cronbach’s alpha varied between 0.55 and 0.76, with higher values in clinical samples compared to controls. The test-retest reliability was good, and the test could discriminate between groups with different levels of traumatisation, supporting its discriminant validity. The Swedish translation of the ETI exhibited similar psychometric properties as both the original version and translations.

Paper III examined how childhood trauma and psychiatric comorbidity affect adult functioning - independently, through mediation or moderation. This was done in two samples consisting of 414 psychiatric outpatients and 100 non-clinical participants respectively. The study found that in clinical samples, both childhood trauma and comorbidity affected functioning, with comorbidity partially mediating the effect of trauma. In the non-clinical sample, only comorbidity was associated with functioning. No moderation effects were present in either sample.

Paper IV explored predictors of functioning and their combined predictive power. Temperament and character traits, attachment styles, childhood trauma and psychiatric comorbidity including personality disorders were assessed in 137 psychiatric outpatients. While many variables individually predicted functioning, only the temperament trait Harm Avoidance and the character trait Self-Directedness remained significant predictors in a multiple regression analysis, explaining about one-third of the variance. These findings emphasize the role of personality traits in understanding and predicting the functioning of psychiatric patients.

In summary, the studies in this thesis support that functioning and childhood trauma can be measured with good reliability using the SDS and ETISR-SF, and that personality factors may be important predictors of functioning in psychiatric patients.