Author: Matthew Iasiello
Iasiello, Matthew, 2023 Investigating the dual-continua model of mental health: Assessment of mental wellbeing in the context of psychological distress, Flinders University, College of Nursing and Health Sciences
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The dual-continua model of mental health suggests that mental illness and mental wellbeing reflect distinct continua, rather than the extreme ends of a single spectrum. This conceptualisation of the relationship between mental wellbeing and mental illness has significant potential implications in the way we promote mental health, and prevent, treat, and recover from mental illness. However, little is known about the evidence validating the model, and whether this evidence supports the implications that have been proposed in the literature. This thesis includes a systematic review examining the evidence and implications of the dual-continua model, which served as a framework for three subsequent studies aimed at addressing gaps in the literature. While the systematic review identified support from the dual-continua model, two key gaps were identified related to the role of mental wellbeing as a predictor of recovery from mental illness, and the importance of assessing mental wellbeing as a complement to assessment of distress or dysfunction. The studies included in the current thesis are: (1) a longitudinal cohort study investigating the role of wellbeing in recovery from clinical mental illness, (2) a meta-analytic factor analysis of the structure of a wellbeing measure, the Mental Health Continuum – Short Form (MHC-SF) in clinical and non-clinical populations, and (3) a cross-sectional analysis of measurement invariance of the MHC-SF in distressed and non-distressed members of the general population. The first study used a representative 10-year longitudinal cohort study (n=1,723) of individuals with a diagnosed affective disorder, to investigate whether level of wellbeing predicted recovery. Individuals who maintained or gained the highest levels of mental wellbeing were 27.6 and 7.4 times, respectively, more likely to recover when compared to those who maintained the lowest level of mental wellbeing. This study reinforced the need to assess mental wellbeing in clinical settings, leading to the following two studies in the thesis. The second study used data extracted from 26 studies (n=108,603) to investigate the factor structure of the MHC-SF, finding empirical and theoretical support for the hierarchical model which taps into a general wellbeing factor, and three lower-order characteristics of emotional, psychological, and social wellbeing. This model performed similarly across clinical and non-clinical populations, however a moderator analysis indicated that there were significant differences in the item loading on the lower-order factors. This result led to the final study, which investigated invariance of the MHC-SF to participant distress. A large Australian sample (n=8,406) was used to demonstrate that the MHC-SF is metric non-invariant, indicating that wellbeing items may be interpreted and valued differently in distressed and non-distressed individuals. This finding, in combination with the previous study indicate that total and subscale scores of the MHC-SF may not be equivalent between clinical or distressed and non-clinical populations, and caution is required when making comparisons between them. The thesis concludes that the dual-continua model of mental health is valid and has a range of important implications for mental health research and practice, however a need remains for improved assessment tools that are invariant to participant distress or clinical status.
Keywords: dual-continua model of mental health, wellbeing, mental illness, assessment,
Subject: Health Sciences thesis
Thesis type: Doctor of Philosophy
Completed: 2023
School: College of Nursing and Health Sciences
Supervisor: Emeritus Professor Eimear Muir-Cochrane