An investigation of body mass distributional changes in Australia, 1995-2017/18

This study investigates changes in the distribution of body mass for adult Australians between 1995 and 2017/18. Using three nationally representative health surveys, we first apply the parametric generalised entropy (GE) class of inequality indices to measure the level of disparity in the body mass distribution. Results from the GE measure reveal that, while growth of body mass inequality is a population-wide experience, demographic and socio-economic factors explain only a modest portion of total inequality. We then apply the relative distributions (RD) method to garner richer insights on changes to the body mass distribution. The non-parametric RD method reveals growth in the proportion of adult Australians falling into the upper deciles of the body mass distribution since 1995. Then, hypothetically keeping the shape of the distribution unchanged, we discern that body mass increases across all deciles of the distribution (location effect) is an important contributor to the observed distributional change. After removing the location effect, however, we find a non-trivial role for distributional shape changes (growth of the proportion of adults at the upper and lower parts of the distribution as the proportion in the middle diminish). While our findings support current policy directions that target the population as a whole, factors driving shape changes to the body mass distribution also need consideration when designing anti-obesity campaigns, especially when aimed at women.