Reassessing measures of population ageing as a tool for driving healthy longevity
Authors: Martin O'Flaherty, Anna Head
Journal: The Lancet Healthy Longevity (2022)

Demographic changes and ageing population structures raise societal challenges, such as smaller working age populations supporting higher health and pension expenditures. The old-age dependency ratio (OADR) is an established, simple, and widely used measure of the ageing burden. However, it is essentially a measurement whereby only age matters. Times have changed, and age is no longer a good predictor of health and functioning levels. The study in The Lancet Healthy Longevity by Vegard Skirbekk and colleagues1Skirbekk V Dieleman JL Stonawski M Fejkiel K Tyrovolas S Chang AY The health-adjusted dependency ratio as a new global measure of the burden of ageing: a population-based study.Lancet Healthy Longev. 2022; 3: e332-e338Summary Full Text Full Text PDF Scopus (1) Google Scholar presents a simple and elegant idea to help us to better capture the effect of how populations are ageing with regards to health and function. The authors developed a new measure in this paper: the Health-Adjusted Dependency Ratio (HADR). This measure explicitly incorporates global and country-level disease burden information alongside demographic data to estimate a population dependency ratio. Other existing measures can be used to capture healthy lifespans, such as health-adjusted life expectancy or disability-adjusted life years. However, HADR might better capture the complex dynamic of disease accumulation, because earlier onset of disease and the complex transitioning to different stages of accumulation of disease before death both powerfully influence lifespan and function. The critical innovation with this HADR measure is the use of equivalent age: the age at which an average person in a particular country has the same ageing-related disease burden as an average global 65-year-old in 195 countries. The findings showed that the HADR indicator provides different country rankings than the OADR, suggesting that younger populations are not always healthier, and thus their health and social care needs will vary. For example, in 2017, Japan had an OADR of 0·49 (approximately two working age adults for every person >65 years), the OADR in Uzbekistan is 0·07 (approximately 14 working age adults for each adult >65 years), yet the HADR is 0·17 (approximately six healthy adults for each dependent adult) in both countries, suggesting a similar ageing burden. Furthermore, the HADR correlates better with health-care expenditure, broadly consistent with varying burden of premature disease across countries. The HADR includes a broad range of diseases; most of them are highly prevalent and most, such as cardiovascular and respiratory diseases, injuries, some cancers, and probably 40% of dementia cases, could be prevented by targeting common risk factors such as blood pressure, obesity, poor diets and air pollution.2Livingston G Huntley J Sommerlad A et al.Dementia prevention, intervention, and care: 2020 report of the Lancet Commission.Lancet. 2020; 396: 413-446Summary Full Text Full Text PDF PubMed Scopus (1557) Google Scholar So, it is not surprising that the HADR showed broad differences across countries and populations, suggesting that many of those differences are broadly driven by differences in modifiable risk factors and the broader social determinants of health. We have evidence, at least in some populations such as the UK and the Netherlands, that not only is the onset of singular chronic conditions occurring at younger ages, but also that the onset of multimorbidity is happening earlier.3Head A Fleming K Kypridemos C Schofield P Pearson-Stuttard J O'Flaherty M Inequalities in incident and prevalent multimorbidity in England, 2004–19: a population-based, descriptive study.Lancet Healthy Longev. 2021; 2: e489-e497Summary Full Text Full Text PDF Google Scholar, 4Katikireddi SV Skivington K Leyland AH Hunt K Mercer SW The contribution of risk factors to socioeconomic inequalities in multimorbidity across the lifecourse: a longitudinal analysis of the Twenty-07 cohort.BMC Med. 2017; 15: 152Crossref PubMed Scopus (68) Google Scholar, 5Singer L Green M Rowe F Ben-Shlomo Y Morrissey K Social determinants of multimorbidity and multiple functional limitations among the ageing population of England, 2002-2015.SSM Popul Health. 2019; 8100413PubMed Google Scholar More importantly, this earlier and faster accumulation of diseases is socially patterned, particularly among working-age adults, with multimorbidity onset among people with greater socioeconomic deprivation in England occurring 7 years earlier than the most affluent.3Head A Fleming K Kypridemos C Schofield P Pearson-Stuttard J O'Flaherty M Inequalities in incident and prevalent multimorbidity in England, 2004–19: a population-based, descriptive study.Lancet Healthy Longev. 2021; 2: e489-e497Summary Full Text Full Text PDF Google Scholar The HADR's use of global average ageing-related disease burden at age 65 years will allow this indicator to adapt to such changes and to better describe future trends in demography and population health. Accepting the signal that the HADR is related to the preventable burden, it can eventually be used to explore regional and subnational differences and disparities across social and ethnic groups, which, by definition, are avoidable. Similarly, the HADR might be sensitive to the effect of prevention strategies and interventions intending to delay disease onset and ameliorate the effect of disease on disability and dependence. Thus, HADR can potentially be a valuable measure to monitor progress on achieving healthy ageing goals and narrowing social inequalities in terms of both health and functionality, as well as informing research and public health action around healthy ageing agendas such as the UN Decade of Healthy Ageing. Methodologically robust health indicators are essential tools.6Murray CJL Lopez AD Production and analysis of health indicators: the role of academia.PLoS Med. 2010; 7e1001004Crossref Scopus (18) Google Scholar However, they are part of a policy ecosystem that decides and prioritises agendas and resource distribution.7Storeng KT Béhague DP “Guilty until proven innocent”: the contested use of maternal mortality indicators in global health.Crit Public Health. 2017; 27: 163-176Crossref PubMed Scopus (44) Google Scholar Understanding the technical features of indicators is important, alongside conversations on how they will be used and how they shape agendas and influence stakeholders. Adopting the HADR for policy purposes will require these conversations, but it is a promising measure that can inform our approach to living longer in better health. We declare no competing interests. The health-adjusted dependency ratio as a new global measure of the burden of ageing: a population-based studyThe OADR probably overestimates the burden of population ageing in many demographically older countries and underestimates the ageing burden in many demographically younger countries, which implies that the challenges associated with ageing are more universal than previously thought, and that the world cannot easily be divided in a young and an old groups of nations. Full-Text PDF Open Access