Disability-free life expectancy between 2002 and 2012 in England: - PDF document

Disability-free life expectancy between 2002 and 2012 in England: trends differ across genders and levels of disability Benedetta Pongiglione ∗ 1 , George B. Ploubidis 1 , and Bianca L. De Stavola 2 1 UCL Institute of Education, Centre for Longitudinal Studies 2 UCL GOS Institute of Child Health Abstract Background: The aim of this work is to assess how disability-free life expectancy (DFLE) has evolved over the past decade in England distinguishing four levels of disability, and to propose possible explanations for observed changes over time and differences between genders and disability severity levels. Methods: We used data from the English Longitudinal Study of Ageing and considered both cross-sectional and longitudinal samples, interviewed from 2002 to 2012 (at 6 waves). Disability was defined according to the WHO’s International Classification of Functioning, Disability and Health, from which 4 classes were estimated (no disability, mild, moderate and severe), in correspondence to each wave, using latent class analysis. DFLE was estimated at the first and last wave by applying Sullivan’s method, and years lost to disability (YLD) were estimated in a second stage to perform individual-level analyses of the relationship between changes in YLD between 2002 and 2012 and Body Mass Index (BMI) measured in 2002 and year of birth. Results: Changes in DFLE observed between 2002 and 2012 differed across gender and disability classes. Severe and moderate disability declined for women, while their mild disability increased, indicating a dy- namic equilibrium overall. Men experienced worse changes, with stable levels of severe disability and increasing moderate disability. There was evidence of modification of the effect of BMI by year of birth on changes in YLD, such that high BMI resulted particularly detrimental to younger cohorts. Conclusion: Two conclusions emerge from these results: (i) It is important to distinguish between milder and more severe levels of disability because their trends seem to be divergent. (ii) The evidence of in- teraction between BMI and year of birth points towards the need for closely monitoring BMI in younger generations as this appears to be detrimental in terms of their disability experience in later life. Key words: Disability free life expectancy; expansion; compression; older population; England ∗ Corresponding Author: b.pongiglione@ucl.ac.uk 1

Acronyms ADL Activity of Daily Living BMI Body Mass Index DALY Disability-Adjusted Life Years DFLE Disability-Free Life Expectancy DLE Disability Life Expectancy ELSA English Longitudinal Study of Ageing HSE Health Surveys for England IADL Instrumental Activity of Daily Living ICF International Classification of Functioning Disability and Health ICIDH International Classification of Impairments Disabilities and Handicaps LCA Latent Class Analysis ONS Office for National Statistics REVES R´ eseau Esp´ erance de Vie en Sant´ e SMPH Summary Measures of Population Health TLE Total Life Expectancy YLD Years Lost to Disability YLL Years of Life Lost 2

1 Introduction Life expectancy has been used as an indicator of population health for a long time. More recently, with the completion of the “epidemiological transition” in high and low-middle income countries [1], mortality has ceased to be as tied to health as it was before, and life expectancy does no longer fully capture the health status of a population. From the 1960s, with the study of Sanders [2] and Sullivan [3], the assessment and monitoring of population health changes have shifted towards indicators that combine both mortality and morbidity (or disability); these are known as Summary Measures of Population Health (SMPH). With the development and adoption of new population health indicators, evaluations of their trends over time have emerged. Three distinct theories of population health changes have been proposed, namely: compression [4], expansion [5, 6] and dynamic equilibrium of morbidity and mortality [7]. It has often been remarked that empirical evidence supporting any of these theories is scarce. However, there has been increasing interest in the use of health expectancy indicators for public policy and planning and for the evaluation of public health programs over the last decades. Hence, the lack of support for any of the abovementioned theories is not only due to the scarcity of studies, but also to the heterogeneity and discordance of results. In 2003, the results of a decade’s work on health expectancy of the R´ eseau Esp´ erance de Vie en Sant´ e (REVES) project was collected in a book and evidence on theories of population health changes were evaluated [8]. At chapter 18, combining the chronological series available for several European countries, from the 1980s and 1990s, Perenboom et al. [9] showed that Total Life Expectancy (TLE) has been increasing in European countries, but this was not always accompanied by a rise in health expectancy. Health expectancy has increased but not as much as TLE. A closer look indicated an increase in the number of years in mild ill health and a decreasing or stable situation for the number of years in moderate or severe ill health [10]. However, the evidence was not very strong and it is unclear whether the conclusions also hold for more recent years. In the UK and England -where the present study is set- evidence is mixed. The UK is one of the few countries for which time-series of life expectancy and health expectancy have been available since the 1980s [11], and thus it has been possible to study trends over about three decades. Nevertheless, no clear pattern has been found. Between 1981 and 1999, dynamic equilibrium of morbidity was found [11]. Perenboom et al. [9], collecting evidence from UK-based studies, reported that in the UK, between 1980 and 1994 there seemed to be an increase in Disability-Free Life Expectancy (DFLE) for females aged 65 years [12], and handicap-free life expectancy increased between 1976 and 1991, but the trend reversed downward between 1991 and 1994 [10, 13]. A more recent study [14] investigated how various health expectancies have changed in England between 1991 and 2011, and showed that cognitive impairment compressed in absolute terms (i.e. supporting evidence of reduction), self-perceived health compressed in relative terms (i.e. increase in the proportion of life spent healthy), and disability evolved in dynamic equilibrium, with less severe disability increasing and more severe disability declining. Looking at other recent studies focused on the older population and set in different countries (US [15, 16], and Sweden [17]), evidence varied across settings, but some common findings emerged as well. The studies that distinguished mild and severe forms of disability [15, 17], generally agreed in finding a decline in severe forms of disability and a rise in milder levels. The study by Freedman et al., set in the US between 1982 and 2011 [15], found that among women aged 65+ mild disability has increased, while severe disability has decreased in proportional terms, but increased in absolute value. The study by Sundberg et al. [17] of Swedish trends between 1992 and 2011, supported absolute and proportional compression of severe disability among women and expansion among men; it also showed absolute expansion of mild disability 3