Investigation into aspects of the excess body mass phenomenon in Australia

<p dir="ltr">There is an obesity crisis in Australia. According to Australian Bureau of Statistics (2023b) estimates, 31% (3.9 million) of adult Australians were obese in 2017/18; this represents a 63% increase since 1995. The phenomenon is troubling because obesity impacts other areas of life. Health-wise, obesity is a risk factor for several physical and psychological conditions. There are also obesity-related costs that have a major impact on the economy in Australia. Moreover, excess body mass has spill-over effects into the employment/personal sphere when individuals carrying excess body mass experience unfair treatment in the labour market. Thus, the various facets of the excess body mass phenomenon in Australia warrants investigation, which is the focus of this research. This PhD thesis comprises three research papers, each focusing on a distinct aspect of the excess body mass experience in Australia. The findings of the research yield insights into alternative/additional ways to view and tackle the rising prevalence of excess body mass in Australia and its broader impact(s) on the labour market.</p><p dir="ltr">Using three nationally representative health surveys (National Nutrition Survey 1995, National Health Survey 2007/08, and National Health Survey 2017/18), the first research paper (chapter 3) examines changes in body mass in Australia between 1995 and 2017/18 by taking a distribution-centred perspective and empirical strategy. More specifically, the paper investigates changes in body mass inequality using the generalised entropy class of inequality indices. The method of relative distribution is then used to get insights on distributional density changes and their sources. Specifically, the paper seeks to answer the questions on the extent of general (BMI) and central (WHtR) body mass inequality change between 1995 and 2017/18; the role of demographic and socio-economic changes as forces underlying the inequality change; the nature of the body mass distributional density changes; and the role played by the location and shape effects as contributors to the density changes. The results reveal a rise in body mass inequality between 1995 and 2017/18. However, demographic and socio-economic characteristics explain little of the inequality growth. The relative distribution method, on the other hand, discloses growth in the proportion of adults falling into the upper deciles of the body mass distribution. The distributional density changes are not driven by demographic or socio-economic compositional changes in the population of Australia. Decomposing the density changes, the location effect is an important driver across most samples, though the shape effect is more impactful among women.</p><p dir="ltr">The second research paper (chapter 4) evaluates how far away Australia stands from the goal of equality of opportunity in body mass by using the egalitarian justice framework of Roemer (1998). Inequality of opportunity represents inequality due to (circumstance) factors outside the personal control of individuals. Drawing upon cross-sectional 2013 and 2017 Household, Income and Labour Dynamics in Australia (HILDA) survey data, the paper employs mean-based and unconditional quantile regression techniques to measure inequality of opportunity in the total adult population of Australia. The paper also undertakes additional (demographic) subsample analyses to determine the gender and age dynamics of inequality of opportunity in body mass. The paper aims to answer questions on the extent of inequality of opportunity in body mass; magnitude of inequality of opportunity at different quantiles of the body mass distribution; gender and age dimensions to inequality of opportunity in body mass; the more influential circumstance factors; contribution by circumstances factors compared to that of effort factors. Analyses reveal that inequality of opportunity explains a modest share of up to 14% of body mass inequality. Among the circumstance factors, parents’ socio-economic status is the single most important circumstance factor at the clinically risky (upper) part of the body mass distribution. While the level of inequality of opportunity is consistently greater among women than men, there are also signs that inequality of opportunity declines over time. Incorporating effort variables into the empirical scope, the relative contribution by circumstance factors to (explained) inequality remains non-trivial, especially for women.</p><p dir="ltr">The third research paper (chapter 5) explores the broader impact(s) of excess body mass on labour market outcomes in Australia. Drawing on fourteen waves (2006 to 2019) of the HILDA survey, the paper investigates the impact of excess body mass on employment prospects and wages in Australia. The main empirical strategy used is dynamic in nature and, as such, it includes past-period labour market outcomes and past-period body mass as part of its estimation specification. Static specifications are also estimated for comparison purposes. The paper seeks to provide answers to the following research questions: are overweight/obese individuals less likely to secure employment and/or receive lower wages in Australia; does the impact(s) of excess body mass on employment prospects and wages vary by gender; does health-related productivity and/or discrimination play a role to influence the excess body mass-labour market outcome relationship. Analyses reveal less than compelling evidence that individuals carrying excess body mass (as measured by body mass index, BMI) experience diminished employment prospects and/or receive lower wages in Australia. Results from the dynamic correlated random effects specification estimated by probit yields significant associations between excess body mass (BMI as a categorical or continuous variable) and employment for the full sample of adult Australians. However, the finding is not robust to analyses of samples that include self-employed individuals. On the body mass-wages relationship, there is also less than compelling evidence that excess body mass lowers workers’ wages in Australia. Mixed results are obtained when the dynamical specification estimated by the generalised method of moments procedure is implemented. Specifically, an inverted U-shaped association is evident in only some specifications when BMI is included as a continuous variable. Investigating the channels of effect, the findings suggest that the health-related productivity plays a role in affecting the excess body mass-employment relationship for women, but not for men.</p>