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Mortality

Life expectancy at birth in a particular year is a way of summarising age-specific mortality rates in that year.[17] Under Statistics New Zealand’s medium assumptions, the median male life expectancy at birth rises from 76.3 years in 2000 to 83.5 years in 2050, while median female expected longevity grows from 81.1 years to 87.0 years.

Figure 7: Statistics NZ assumes gains to life expectancy slow
Source: Statistics New Zealand, life expectancy at birth, history and medium mortality assumptions

This projected rate of gain is slower than we have seen in the past half century (for example, female longevity grew by 9.8 years from 1950 to 2000, but is expected to grow by only 5.9 years in the next half century). For those aged 65 and 85, the assumed life expectancy gains between 2000 and 2050 are generally greater than those between 1950 and 2000. In the extended projections to 2100, Statistics New Zealand holds the life expectancy constant after 2050.

Table 1: Median life expectancy at birth, at 65, at 85, in the stated year
Years 1900 1950 2000 2025 2050 1950-2000 2000-2025 2025-2050 2000-2050
Males Age Gain
Birth 57.4 67.2 76.3 81.4 83.5 9.1 5.1 2.1 7.2
Age 65   12.8 16.7 20.2 21.8 3.9 3.5 1.6 5.1
Age 85   3.9 5.2 7.3 8.3 1.3 2.1 1.0 3.1

 

Table 1: Median life expectancy at birth, at 65, at 85, in the stated year (continued)
Years 1900 1950 2000 2025 2050 1950-2000 2000-2025 2025-2050 2000-2050
Females Age Gain
Birth 60.0 71.3 81.1 85.3 87.0 9.8 4.2 1.7 5.9
Age 65   14.8 20.0 23.2 24.5 5.2 3.2 1.3 4.5
Age 85   4.2 6.5 8.5 9.4 2.3 2.0 0.9 2.9

Source: Life expectancy at birth from Statistics New Zealand, medium mortality assumption.

Alternative mortality paths

As with fertility, Statistics New Zealand has produced projections based on two alternative assumptions of the future course of mortality: high mortality, where life expectancy in 2050 is 81.0 and 85.0 years for men and women respectively; and low mortality, where life expectancy is 86.0 for men and 89.0 for men and women respectively.

We discuss this issue in some detail below, because future trends in life expectancy, and their underlying causes, have a significant impact on our long-term fiscal projections.

The world’s demographic transition started in North West Europe about 1800, with mortality rates generally trending downwards ever since (Lee 2003).

In New Zealand, there has also been a fall in mortality (a rise in survival), and thus a lift in life expectancy (see Figure 7 above). There are two particular features of this increase in life expectancy.

In 1937, 4% of children would be expected to die before their first birthday.  By 2003, this had fallen by almost a factor of 10 to 0.49%. 

First, there has been a substantial reduction in infant mortality. In 1937, for example, 4% of children (born alive) would be expected to die before their first birthday. By 2003, this had fallen by almost a factor of 10 to 0.49%. Similar reductions have occurred at all ages up to 10.

Second, death rates have also reduced substantially during the middle stages of life. Although the reduction is not as dramatic as in the early years of life, it is still substantial and is two to four times lower in 2003 than in 1937.

The combined impact of the lower death rates in early and middle age and a continuing rise in the oldest age to which people live results in what demographers refer to as a “rectangularisation” of the survival chart: far more people survive into old age, and indeed into very old age. This is happening at a faster rate than the increase in the age of the oldest.

While current mortality trends are clear, as yet we do not have full knowledge of what is causing this decline in death rates, what sorts of lives people are leading, especially in later life and whether the trends of the recent past will continue, or reverse. A recent (economics) paper suggests that the decline in mortality rates is ultimately determined by the application of scientific advance and technical progress (some of which is induced by income and facilitated by education).[18]

“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.”

There are many different theories and a consensus is yet to emerge, especially about what is to happen in the future. Quoting Riley, Oeppen and Vaupel (2002) 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.

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. Most of the developed world has probably attained most of the potential reductions in mortality due to reductions in infectious diseases and improved nutrition.

Thus, the continuing reductions in mortality seen in the developed world in recent years are the result of reductions in chronic and degenerative diseases, such as heart disease and cancer.

What of the future? Oeppen and Vaupel are at the optimistic end: they predict no decline in the rate of increase in life expectancy for the foreseeable 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 a remarkable 109 years by 2100.

More conservative predictions, such as those of Lee and Carter (1992), still see life expectancy reaching 90 years by 2100.

Studies undertaken for the Australian Productivity Commission in its work on the economics of population ageing in Australia produced projections of life expectancy that are in excess of the official estimates of the Australian Bureau of Statistics (ABS).[19]

There are, however, other more pessimistic views about the future prospects for mortality and morbidity. Olshansky et al (2005) are critical of those studies that predict life expectancy on the basis of extrapolating the past. As they put it:

Given that past gains in life expectancy have largely been a product of saving the young, and since future gains must result from extending life among the old, another quantum leap in life expectancy can occur only if the future is different from the past.[20]

They prefer an approach that relies on trends in health and mortality that can be observed in the current adult population. On this basis, they examine the effect of one health condition – obesity – on future trends in life expectancy in the United States. They find that current levels of obesity are likely to increase mortality substantially across the age spectrum, which will, in turn, lead demographers to revise downwards their estimates of life expectancy at birth.

Statistics New Zealand uses its median mortality assumption to drive the official Series 5.  This may be on the conservative side when compared with some assumptions being used by other agencies.

Statistics New Zealand uses its median mortality assumption to drive the official Series 5. This may be on the conservative side (relatively low longevity outcomes) when compared with some assumptions being used by other agencies in their long-term work.

Statistics New Zealand’s low mortality (higher longevity) assumption has a greater proportion of elderly, a relatively smaller labour force, and a larger population by 2050 (up by 2.3%).

Assuming high mortality (lower life expectancy) will reverse these differences from the base case. The labour force would be proportionately larger, while the population in 2050 would be smaller.

Net migration

Finally, Statistics New Zealand assumes that migration settles at a net figure of 10,000 immigrants from 2009 onwards (0.24% of the population in that year). Typically, we have a net inflow of people in their late teens and 30s and 40s, but a net outflow of people aged in their 20s. The horizontal lines in Figure 8 are the averages for the periods covered by the lines and show that this assumption is plausible given recent trends.

Figure 8: Projected long-term net migration follows recent averages
Figure 8: Projected long-term net migration follows recent averages.
Source: Statistics New Zealand. Annual net permanent and long-term migration.

Notes

  • [17]Life expectancy at birth (or at age x, more generally) estimates the number of years a person can expect to live beyond birth (age x), based on the age-specific mortality rates of the population in a given year. Only if these mortality rates remained constant over time would the life expectancy at birth match the actual experience of people born in that year.
  • [18]Cutler, Deaton and Lleras-Muney (2006)
  • [19]Booth and Tickle (2003). For example, they estimate female life expectancy at birth in 2027 in Australia to be 88.1 years, compared to an ABS projection of 85.4 years.
  • [20]Note, however, that in New Zealand the fastest absolute and relative declines in mortality in the last 20-30 years have occurred in the oldest ages.
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