Theories of the future course of mortality and morbidity

There are many different theories and a consensus is yet to emerge about where mortality and morbidity are headed. Oeppen and Vaupel (2002, p. 1030) note:

Mortality improvements result from the intricate interplay of advances in income, salubrity, nutrition, education, sanitation, and medicine, with the mix varying over age, period, cohort, place and disease.

Like many countries’ official population projections, those for New Zealand assume that the recent trends in mortality reduction will eventually taper off.[40]

There are, however, studies in the literature that question whether this will be the case. Oeppen and Vaupel, for example, are at the optimistic end. They predict no decline in the rate of increase in life expectancy for the future, with a continuation of a rate of increase of about 2.4 years per decade. This would see life expectancy at birth reach 97.5 years by the middle of the 21st century and 109 years by 2100.

Booth and Tickle (2003), in a study undertaken for the Australian Productivity Commission’s work on the economics of population ageing in Australia, have produced projections of life expectancy that are in excess of the official estimates of the Australian Bureau of Statistics (ABS). They estimate female life expectancy at birth in 2027 in Australia to be 88.1 years, compared with an ABS projection of 85.4 years.

There are also pessimists. Olshansky et al (2005) are critical of those studies that predict life expectancy on the basis of extrapolating the past. They prefer an approach that relies on trends in health and mortality that can be observed in the current adult population, which they suggest will lead demographers to revise downwards their estimates of life expectancy at birth.

Lee (2003) cites two separate stages to the decline in mortality. The first stage, starting in around 1800 in Europe, involved reductions in contagious diseases and infectious diseases spread by air or water. Personal hygiene improved (boosted by increases in income), as the germ theory of disease became more widely accepted. Improvements in nutrition were also helpful. The developed world has probably already experienced most of the potential decreases in mortality due to reductions in infectious diseases and improved nutrition. Cutler, Deaton and Lleras-Muney (2006) reach similar conclusions.

Source: Ministry of Health

Figure 6.2 shows the relationship between age and average government health expenditure per person in New Zealand in the financial year 2003/04. Public health covers areas such as health protection, health promotion and disease control. Disability support services include items such as home support, residential care, and equipment, while personal health includes primary, secondary and tertiary medical care.

Per capita expenditure on personal health and disability support services increased with age in 2004, though the most pronounced increases occur with disability support services. For people aged 85 and over, 61% of health expenditure in 2004 was accounted for by disability support services.

Why does health expenditure increase with age? International research suggests that people in poor health need more health care than people in good health, and that the prevalence of poor health, particularly chronic disease and associated disability, rises with age.

Studies in the United States and Canada have found that, on average, people who are about to die make greater use of health services than those who are not. So “distance to death” can predict health expenditure better than “distance from birth” (age, in other words). The link between distance from death and expenditure is especially strong for acute care (Lubitz and Riley, 1993; McGrail, Green, Barer, Evans, Hertman and Normand, 2000; Miller, 2001; Yang, Norton and Stearns, 2003).

An increase in life expectancy means that there has been a change in the health status of the population. There is an unsettled debate in the literature on what is happening, and what is likely to happen in the future, to health status. The first bar in Figure 6.3 represents a life before the increase in life expectancy. There are three broad possibilities for changes in health status, which are illustrated in a stylised form in the lower three bars. In each case, they take as given an increase in life expectancy: people are, on average, living longer. The question they seek to answer is whether those extra years of life are, to put it crudely, lived in “good” or “bad” health.[41]

The first, and most optimistic, scenario is that health is improving across the board. This is known as a “compression of morbidity”:people both live longer and have fewer years of bad health.

The second is a “dynamic equilibrium” (also known as “healthy ageing”): the absolute period of bad health stays the same, but falls in relative terms as the absolute period of good health increases.

The final and most pessimistic scenario is known as an “expansion of morbidity”: the absolute period of good health stays the same, with all the increased years of life expectancy being in poor health. A severe expansion of morbidity would see the absolute period of good health reducing.

It is difficult to predict the net effect of medical progress on age-specific disability rates. Some new technologies have led to increased disability rates. The standard example is coronary care, which has reduced the case fatality of heart attack, but in so doing has created an “epidemic” of heart failure.

Source: The Treasury

Other technologies, however, such as drugs to reduce hypertension (the major risk factor for stroke), have helped reduce disability rates. Similarly, it is difficult to predict the net effect on disability of conflicting population health trends such as increasing obesity and declining smoking rates. The only way to resolve the uncertainty is to look at longitudinal data on disability.

New Zealand evidence on disability trends

There have been two recent studies of trends in disability in New Zealand.

Graham et al (2004) use data from two observations, one in 1981 and the other in 1996, to evaluate the evidence for the three theories of health change. They find that the “dynamic equilibrium” scenario provides the best fit to the New Zealand data.

Tobias et al (2004) use data from two surveys of disability conducted in 1996 and 2001, after each census, to test for trends in health status. They find mixed evidence. Their method divides expected life into four discrete periods:

• disability-free life expectancy
• disability not requiring assistance (level 1 disability)
• disability requiring non-daily assistance (level 2 disability)
• disability requiring daily assistance (level 3 disability).

Over the five years between the two censuses, life expectancy at birth for males increased by 1.9 years, to 76.3 years; while for females, the increase was 1.5 years, to 81.1 years.

Table 6.1 breaks down the increase in expected life into the four stages. The results are different for males and females. For males, the vast bulk of the increase can be expected to be spent in the state of highest disability. This supports an “expansion of morbidity” theory. For women, however, there is actually a decline in the period spent in the highest level of disability, with increases in disability-free years as well as periods of moderate disability.

International evidence

Bryant, Teasdale et al (2004) report on a systematic review of international longitudinal studies.[42] Census data from Australia appear to imply that disability rates have risen. The highest-quality studies, covering the longest periods, however, have been conducted in the United States. These studies all suggest that disability rates have declined significantly.

Robine and Michel (2004) suggest that population-wide studies might be masking some significant trends through time and in sub-groups of societies. They tentatively suggest that a four-stage process can explain the apparently inconclusive evidence, as follows:

1. an initial increase in survival rates of sick people, leading to an expansion of morbidity
2. control of the progression of chronic diseases, which produces a “dynamic equilibrium” between a fall in mortality and an increase in disability
3. an improvement in the health status and behaviours of new cohorts of older people, which produces a compression of morbidity
4. the eventual emergence of very old and frail populations, which would be represented as a new expansion of morbidity.

Synthesis

Putting these competing theories and the data from New Zealand and overseas together is not an easy task. The forces at work are complex and not completely understood.

From these studies, it is reasonable to assume that, in the future, the incidence of disability will decline as the population ages, meaning that people will be living longer and healthier lives.