The central objective of this thesis was to explore the health promotion potential of interventions that enhance individual well-being and their delivery via the internet. The thesis started with a literature review integrating two fields of research, positive psychology and internet interventions (Paper 1). The review identified online positive psychology interventions (OPPIs) as having health promotion potential, through the enhancement of well- being and reduction of mental illness symptoms, but more research was required to clearly establish their efficacy. A randomized controlled trial (RCT) was conducted to test the efficacy of an OPPI (strengths intervention) compared to a problem solving intervention and a placebo control (Paper 2). Participants (N = 160, 83% female, mean age 37 years) completed measures of well-being and mental illness at pre-assessment, post-assessment and 3-month follow-up. Attrition from the study at 3-month follow-up was high (83%), highlighting a recurring issue in internet intervention research. The results provided some support for the enhancement of subjective well-being (Personal Wellbeing Index – Adult version; PWI-A), but not for illness symptoms reduction, via an online fully automated, self- guided, strengths intervention. The next study (N=623, 81% female, mean age 39.9 years) was a RCT measuring well-being and illness symptom outcomes for three intervention groups (strengths, eCoach and mindfulness) compared to a waitlist control (Papers 3 and 4). Self-report measures were administered at baseline, post-intervention, one and three month follow-up, and included the PWI-A, Satisfaction With Life Scale (SWLS), Modified Differential Emotions Scale (mDES) Psychological Well-Being (PWB), Mental Health Continuum – Short Form (MHC-SF), Depression Anxiety Stress Scale-21 item version (DASS-21), Ten Item Personality Inventory (TIPI), Mindfulness Awareness Attention Scale (MAAS), and physical health. The baseline data for the study was presented in Paper 3, which explored the prevalence of well-being and the psychometric properties of the Mental 1Health Continuum – Short Form (MHC-SF), a relatively new measure of well-being. The MHC-SF demonstrated good internal consistency, test re-test reliability, incremental and construct validity. The data supported a three factor structure of well-being, with a modified social well-being subscale. Based on the MHC-SF well-being categories, ‘flourishing’ participants (45.5%) had lower mental illness symptoms, and higher mindfulness and physical health outcomes compared to participants with moderate (46.4%) or languishing (8.1%) well-being. In Paper 4, the longitudinal findings and the potential moderating effects of human support (i.e., the eCoach group were offered email support as they completed the strengths intervention) and baseline levels of well-being and depression symptoms were presented. Compared to waitlist, the Strengths and eCoach participants had significant increases on a range of well-being measures; and the eCoach and Mindfulness groups had a significant reduction in depression and anxiety symptoms respectively. Moderating effects were found (e.g., increases in life satisfaction for Mindfulness group participants with elevated depression symptoms) highlighting the importance of tailoring interventions to individual characteristics. Overall, the thesis findings provide support for the notion that well- being can be intentionally enhanced and that evidence-based interventions can be effectively delivered online as part of an accessible and sustainable health promotion and illness prevention strategy.
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