Measuring and Monitoring Success in Compressing Morbidity

The Compression of Morbidity paradigm, which was presented as an hypothesis in 1980 (1), noted that most illness was chronic and occurred in later life and postulated that the lifetime burden of illness could be reduced if the onset of chronic illness could be postponed and if this postponement could be greater than increases in life expectancy. Figure 1 illustrates this concept. Estimated present lifetime morbidity is portrayed with three possible future scenarios: life extension, shift-to-the-right, and compression of morbidity. The lines represent the length of life, and the shaded triangles depict lifetime morbidity. Two arrows are shown for each scenario: The left arrow represents the median age at onset of chronic morbidity and therepresents the median age at death. Alternative health futures are determined by the relative movement of these arrows over time. If the arrows separate, lifetime morbidity increases, and if they come closer, morbidity is compressed. In each scenario, some extension of life expectancy is envisioned. The illustrative use of age 55 years as the present age of onset of chronic morbidity is drawn from our data showing this to be the median age of detectable chronic disability (2). Figure 1. Possible scenarios for future morbidity and longevity. In 1980, most demographers and health policy workers believed that the life extension scenario was occurring and was the most likely, and most unfortunate, future for health. As medical progress increasingly prolonged life, those extra months and years would be spent in poorer health. The process was termed the failure of success (3). The Compression of Morbidity represented a positive concept, with the ideal of a long life with a relatively short period of terminal decline. Initially, the concept was sometimes portrayed as naively optimistic and, perhaps, a threat to the preparation required to care for ever-larger elderly populations (4, 5). A problem in 1980 was the lack of data on trends in morbidity; such data would have required serial population surveys with similar methods, and these were not available. There was not even agreement on the definition of morbidity, nor is there now. It seemed reasonable in 1980 to postulate that lifetime morbidity had been rising with the emergence of chronic illnesses, but it could be argued that this period was ending with declining incidences of major chronic illnesses, such as cardiovascular disease (1). The Compression paradigm focuses attention on the quality of life over its quantity and considers morbidity as a lifetime cumulative area-under-the-curve concept rather than just a cross-sectional particular point of time, such as a specific age. It suggests that the national burden of illness may be reduced by postponing the onset of infirmity. Thus, the national illness burden that is increasing because of the growing number of elderly persons in the population may be offset, at least in part, by a lower average illness burden for the individual, with positive consequences for the stability of the health care system. This paper draws on recent data from national surveys, observational longitudinal studies, and randomized, controlled trials to bring together the current evidence for morbidity compression in the United States and to outline the research agenda for the continued monitoring of trends in morbidity and disability. Given appropriate data, the Compression hypothesis can be tested by using age-specific disability rates or cumulative lifetime disability as surrogates for the less easily quantitated morbidity rates. Trends in age-specific disability can then be compared with trends in age-specific mortality, and trends toward a postponed point of incident disability can be compared with trends toward a postponed age at death. If age-specific disability declines faster than age-specific mortality, then compression is established. Even better, if given serial cohorts of longitudinal data, trends in cumulative lifetime disability could be assessed. In addition, if disability could be postponed by specific interventions (such as exercise, weight control, total joint replacement, influenza vaccination, or smoking cessation) by more than projected increases in the length of life from these interventions, then strategies for reduction in the national burden of illness by dissemination of these interventions would become possible. Trends in Mortality Since morbidity compression depends on the relative trends in morbidity and mortality, trends in life expectancy must be examined. From 1980 to 1998, life expectancy (U.S. data; both sexes combined) rose at a rate of 0.150 year per year, for an increase of 2.7 years, to 76.6 years, somewhat slower than in the two previous decades (6). The more relevant number, however, is life expectancy from age 65 because it excludes early-life mortality. Life expectancy from age 65 rose at a rate of only 0.066 year per year, for an increase of 1.2 years over 18 years, to a life expectancy of 82.7 years; this is a slightly lower rate of increase than in previous decades. From age 85, life expectancy rose by 0.017 year per year for an increase of 0.3 years or only about 4 months over 18 years. If present trends continue, gains in life expectancy after 65 years of age will remain modest. Because of larger birth cohorts and an increasing proportion of persons surviving to age 65, however, the number of elderly persons will increase markedly. Present trends, however, will not continue indefinitely. Barring discovery and dissemination of a breakthrough in understanding of the basic science of aging, the rates of increases will continue to slow. Constant decreases in mortality rates, about 1% per year, yield diminishing increases in terms of life expectancy over time because of the mathematical relationship between the two statistics; the absolute value of the mortality rate change decreases over time (7). This can be seen with the point of paradox, in which life expectancy from birth, rising more rapidly, exceeds life expectancy from age 65 years, rising more slowly, after an intersection point at a life expectancy of 87.8 years in the year 2076. Because this is not possible, present trends cannot continue indefinitely. Trends in Morbidity Over the past two decades, it is possible that a great natural experiment occurred in which preventive measures, which are most relevant to postponement of morbidity, had been broadly implemented. On a national basis, there could have been massive reductions in health risk factors, such as cigarette smoking, obesity, and sedentary lifestyle. Then, with emerging data on trends in disability, particularly from the National Long-Term Care Survey (NLTCS) (8) and the National Health Interview Survey (NHIS) (9), we could assess the benefits from these changes against changes in mortality. Unfortunately, although smoking did decrease significantly, the prevalence and amount of obesity increased, and a trend toward more sedentary lifestyles continued. Over the last two decades, therefore, lifestyle changes probably did not play a major role in compression of morbidity. Nevertheless, compression of morbidity is occurring, and at a relatively rapid rate. In the NLTCS data (Table), disability in persons older than 65 years of age decreased from 26.2% to 19.7% from 1982 to 1999, a decrease of approximately 2% per year and substantially greater than the decreases in mortality rates over this period, which declined at about 1% per year (10). The decline was seen both in activities of daily living disability and instrumental, more complex activities of daily living. It has been argued that a decline in age-specific disability of 1.5% per year would be sufficient to maintain the solvency of Medicare for at least 70 years (11). Moreover, the declines in disability in the NLTCS accelerated in the past 5 years of observation and began to be seen in minority as well as white subpopulations (8). Data from the NHIS from 1982 to 1996 show strikingly similar declines in disability, again with an accelerated rate of decline in more recent years (9). Table. Long-Term Trends in Disability Recently, Freedman and colleagues (12) performed a systematic review of 16 studies of trends in disability and found them consistent in the finding of declining disability trends. Thus, the literature, although of uneven quality, shows consensus. Only the NLTCS data had a sample of all Medicare-eligible persons, both institutionalized and not; covered a sufficient time period (1982 to 1999); and had well-defined disability measures. This is the single best study (Figure 2) (13). Figure 2. Recent trends in disability among older Americans. NLTCS NHIS ADL IADL The reasons for the decline in disability seem to be multifactorial, with no single identifiable cause. There may have been contributions from reductions in cigarette smoking; medical advances, such as better treatment of hypertension, diabetes, coronary artery disease, and rheumatoid arthritis; total joint replacements; and medical preventive measures, such as colon cancer screening, influenza and pneumococcal vaccines, and cardiac-dose aspirin (10). It might be that rising expectations for healthier aging became self-fulfilling, perhaps through a mechanism of perceived self-efficacy (14). The association between level of education and health is strong, and self-efficacy might at least partly explain this association; education levels in the elderly rose substantially over the past two decades (15). Social factors do not seem to have played a role; access to care has not improved, and access to prescription drugs may have become more difficult (10). Whatever the reasons, compression of morbidity is currently occurring at the population level in the United States. Health Risks and Lifetime Disability Longitudinal studies of the relationships of lifestyle risk factors to subsequent disability levels in advantaged elderly pop