Melbourne School of Population and Global Health - Theses
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ItemA study of the effect of adverse psychosocial work stressors on health and mortality( 2021)The working environment is central in the lives of individuals in employment, influencing health outcomes including psychological and physical well-being. Psychosocial work stressors are common exposures in the workplace and are important and modifiable determinants of health and health behaviours. There is broad agreement in the literature that exposure to adverse psychosocial work stressors, such as high job demands, low job control, low job security and high effort-reward imbalance are associated with poor health outcomes. All of these exposures are, in turn, associated with unhealthy behaviours such as smoking, alcohol consumption, poor diet and inactivity, and to the development of hypertension, cardiovascular disease, diabetes, musculoskeletal disorders and depressive disorders. Psychosocial work stressors have been identified as significant emerging risks linked to global changes in the structure, organisation and management of work during previous decades, presenting pressing challenges to occupational health and safety and workplace health, in general. Most of the literature in this area assesses disease incidence or other morbidity outcomes, with a growing number of studies focusing on mortality. However, whether exposure to these psychosocial work stressors associated with adverse health outcomes translates into increased mortality remains unclear, and barriers to making causal interpretations about the relationship between psychosocial work stressors and health persist, mostly due to inherent biases in the methodology across studies. In this thesis, the effect of exposures to psychosocial work stressors in the working environment such as job control, job demands, job strain, long working hours, job insecurity and shift work on health and mortality were investigated. A comprehensive systematic review including meta-analyses of the epidemiological research was conducted. Panel data from the Household, Income and Labour Dynamics in Australia survey was used to capture natural experiments of psychosocial work stressors associated changes in health and well-being, and mortality to investigate whether and how the effect of psychosocial work stressors on mortality differ in relation to demographic and socioeconomic characteristics. The initial focus of the research included establishing and quantifying the risks associated with adverse psychosocial work stressors, which workers are commonly exposed to in the workplace, on mortality. The final study in the PhD focused on understanding the exposure-outcome dynamics. The dynamics of the connexions between psychosocial work stressor perceived job control and general health, a strong predictor of future morbidity and mortality, were investigated for evidence of a causal relationship. The first study showed that improving the quality of work might contribute to better health and well-being and decrease the effect of psychosocial work stressors on all-cause mortality and cardiovascular disease mortality. If this observed association is causal, then policy and practice interventions to improve job control could contribute to reductions in mortality. Study II adds to the growing body of evidence showing an effect of adverse psychosocial work stressors on mortality. Study III showed that long-term exposure to low job control and job security was associated with increased risk of all-cause mortality. In Study IV, the dynamics of job control and general health were explored for evidence of a causal relationship using three complementary longitudinal modelling approaches. This study, using improved causal inference methods than previous research, showed that increased job control was strongly associated with increasing general health. Although the estimates for the single measures suggest modest increases in the risk of death and poor health, this translates to large population impacts because the exposures are relatively common across the working population. Thus, reducing exposure to psychosocial work stressors associated with mortality and poor health could have considerable public health benefit. Awareness by stakeholders, government and organisations of the implications of the adverse effects of psychosocial work stressors on health and mortality in workplaces; and the availability appropriate, evidence-based work stress interventions to reduce the exposure to work stressors might contribute to better health and well-being, reduce sickness absence and presenteeism to the benefit of workers, workplaces and society.
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ItemHow do socio-economic characteristics influence the effect of disability acquisition on mental health? An analysis of effect modification and mediation( 2019)Background People with disabilities in Australia experience poorer mental health than people without disability. However, the mechanisms by which disability leads to poor mental health are inadequately understood. This PhD thesis aims to form a better understanding of how people’s socio-economic circumstances influence the effect of disability acquisition on mental health. Elucidating the causal mechanisms underpinning this relationship will inform the development of effective public health and social policies to improve the mental health of people with disabilities. Methods I used data from the Household, Income and Labour Dynamics in Australia Survey – a large nationally representative longitudinal dataset – to quantify the effect of disability on mental health and to examine the socio-economic mechanisms leading from disability acquisition to poor mental health. I identified adults who acquired a disability during their participation in the survey and used data both before and after they acquired the disability to estimate the causal effect of disability on mental health. Firstly, I conducted analyses of effect modification, examining a wide range of different socio-economic factors to determine whether they influenced the magnitude of the effect of disability acquisition on mental health, using inverse probability weighting and fixed effects models to better control for confounding. Secondly, I conducted causal mediation analyses to further examine the socio-economic mechanisms leading from disability to poor mental health, using sequential mediation analysis to examine a broad range of socio-economic characteristics and an interventional mediation approach to quantify indirect effects operating through two distinct socio-economic characteristics: employment and income. Finally, I examined the indirect effect mediated by employment in greater detail, further decomposing the natural indirect effect through employment to estimate the proportion attributable to interaction, mediation and their joint effects. Results There is a clinically significant and large effect of disability acquisition on mental health. The analyses of effect modification provided evidence that the magnitude of the effect differed according to people’s socio-economic characteristics, with greater effects observed for more disadvantaged groups. The mediation analyses provided additional evidence that socio-economic characteristics contribute to the effect of disability acquisition on mental health. A third of the effect was found to be mediated by material socio-economic factors such as employment, income, wealth, financial hardship and housing characteristics, and a further investigation of the indirect effect through employment and income highlighted employment (but not income) as an important contributing factor, explaining 11% of the effect alone. Finally, further decomposition of the indirect effect through employment suggested that the mediated effect was due to interaction between disability and employment, rather than pure mediation. Conclusion The findings of this thesis highlight the importance of the social determinants of health in generating mental health inequalities. Interventions should prioritise addressing the social determinants of health to improve the mental health of people with disabilities and reduce disability-related mental health inequalities. Furthermore, the evidence that employment is a key mediator of the effect of disability acquisition on mental health indicates that policy strategies are needed to target the causes of low employment rates for people with disabilities.