Depression is a common and disabling mental disorder. Empirical studies have shown that depressive symptoms vary substantially according to antecedents and outcome variables. Nevertheless, research is most often reduced to symptom counts and clinical settings. One of the limitations is the lack of knowledge about the presentation of individual symptoms and their association with clinically relevant outcomes, such as severe functional impairment. The heterogeneity of the symptoms may be an important source of information for a better understanding of depression. This thesis aims to produce empirical insights on how individual depressive symptoms relate to severe functional impairment in community-based samples. In this doctoral dissertation, we used symptom-level data from two large epidemiologic studies that are representative of the population of the United States: the Collaborative Psychiatric Epidemiology Surveys (CPES), and the National Health and Nutrition Examination Survey (NHANES). Our results suggest that, in terms of statistical fit, sum-scores functioned almost as efficiently as symptom-level modeling in predicting self-rated functional impairment. However, examining symptoms individually offered a more detailed understanding of depression as a syndrome. For instance, symptom-level analyses revealed that age group moderated the associations of three symptoms with severe impairment. According to our results, middle-aged adults were more prone to feel severely impaired by these symptoms, as compared to adults aged 30 and below and in retirement age. The symptoms were depressed mood, self-criticism, and impaired concentration. Additionally, some symptoms did not have a significant association with high functional impairment in a fully adjusted model. This suggests that the association with impairment runs through other symptoms. In general, we found that cognitive-affective symptoms of depression related consistently to severe functional impairment. Among them, self-criticism emerged as particularly informative for its consistent association with high functional impairment across analyses, and for its effect on other symptoms as revealed by cross-sectional direction of dependence analyses. A practical implication of this is that supporting individuals’ self-worth may protect against the development of depressive symptomatology and its corresponding impact on functioning. Our findings motivate considering a wider range of symptoms, both in terms of severity and content, for further understanding the heterogeneity of depression. Similarly, functional impairment as a core component of severity calls for systematic exploration, and for a more refined measurement. A better characterization of the severity of depression as a continuum is fundamental for theoretical developments in psychopathology, and potentially useful for planning more efficient interventions targeting the most disabling, dominant symptoms.
|Status||Publicerad - 2019|
|MoE-publikationstyp||G5 Doktorsavhandling (artikel)|
- 515 Psykologi