Population estimates and projections for Australia’s very elderly population at state and national level

Abstract

As in many developed countries, the very elderly population (ages 85+) is the fastest growing age group in Australia, with far-reaching economic and social consequences. To effectively plan and budget for the income, aged care and health care needs of the very elderly, accurate estimates and projections are required. There are, however, several obstacles relating to the availability and accuracy of very elderly data. Official population estimates at very high ages in Australia have been found to be too high and fluctuate implausibly over time. International and local studies have found large errors in projected very elderly populations, stemming from inaccurate mortality rate forecasts. This thesis aims to create accurate estimates and projections for Australia’s very elderly population at a state and national level. Various methods for estimating very elderly populations from death counts were assessed for accuracy at both a national and state level. While the Human Mortality Database uses such methods to create estimates for many countries, their accuracy has never been assessed for Australia. Furthermore, little is known, locally or internationally, about their performance at a sub-national scale. In this study, the accuracy of various nearly-extinct-cohort methods were assessed at the Australian national and state level by retrospectively applying them to extinct cohorts and comparing the results against those obtained from applying the Extinct Cohort method. Suitable methods were applied to create very elderly population estimates and death rates for Australia from 1972-2012 by sex, state and at single ages 85-110+. The growth, changes in the age-sex composition and the demographic drivers of growth of Australia’s very elderly population were analysed. Based on these estimates, more reliable death rates were calculated, allowing a detailed study of the changing patterns and trends in Australian adult mortality. Finally, a number of mortality forecasting methods were retrospectively evaluated for their accuracy in projecting adult death rates for Australia over 10 and 20 years ending in 2012. An appropriate method was applied to create projections for the next three decades. It was found that, compared to the official census-based estimates, more plausible and accurate estimates, especially for ages 95+, could be derived from death counts. The Survivor Ratio (SR) method with results constrained to official estimates for ages 85+ produced accurate very elderly population estimates for Australia across the sexes and ages at both a national and state level. Internal migration is sufficiently minor to be ignored. Very accurate state-level estimates could also be derived using a simpler method of apportioning national single-age estimates between the states. Adult death rates in Australia were found to show consistent and regular patterns of decline since the 1970s, with rates of decline decreasing with age. These patterns support the use of simple direct extrapolation methods for forecasting. The Geometric, Ediev and Lee-Carter BMS methods were all very successful in projecting adult death rates and very elderly populations, and differences between them were small. Australia’s very elderly population increased more than four-fold between 1981 and 2012, from 105,000 to 430,000, or from 0.7% to 1.9% of the total population. Accompanying this growth was an ageing of the very elderly population itself, as well as increasing sex ratios. Improvements in survival beyond age 65 and especially beyond age 85 were the main drivers of growth in nonagenarian and centenarian numbers. Australia’s very elderly population is expected to continue growing rapidly over the next 30 years to almost 1.5 million in 2042, or 4.2% of the total population. Centenarian numbers are expected to increase from almost 3,500 in 2012 to over 15,000. South Australia’s very elderly population is projected to grow the least and Western Australia’s the most. Projected very elderly numbers in 2042 are 13% higher than official projections. Official projections of centenarians were, however, 55% higher. These differences stem from overstated official population estimates and understated death rates for the high ages as well as lower assumed declines in death rates in official projections. This thesis presents more plausible and detailed estimates and projections of Australia’s very elderly population at a state and national level based on methods found to be accurate. It is shown that estimation methods based on deaths can be reliably applied at a sub-national level. The analyses improve our understanding of the demographic drivers of growth of nonagenarians and centenarian populations in Australia, nationally and in the separate states. Insights are gained on how the patterns and trends of change in adult mortality in Australia compare to those internationally. This study furthermore contributes new insights into the accuracy of both old and new mortality forecasting methods. An improved understanding of past trends based on accurate population estimates and death rates, combined with more accurate projections based on accurate data and appropriate methods, facilitates effective planning and budgeting for infrastructure, services, aged pension, aged care and health care for the very elderly.