Distinguished Professor James R. Carey is an Entomologist at UC Berkley. He has a long career studying the survival and social structure of species such as medflies. In latter years he has also applied his expertise to human demography and ageing. He has written a number of books and papers on these subjects.
In this 4 minute video, recorded by Basil Gelpke in 2011, he provides his insights on human life span and population growth as an introduction to our study of Life Expectancy and Life Span.
Professor Carey raises a number of topics summarised in the following comments:
"Now is the first time in the history of the Human species for the Old to outnumber the Young"
"Earth's human population has a limit somewhere around 10 billion"
"If we are looking at a human life span of 100 years, we can only reproduce once every 50 years to avoid further increase"
We will expand on these comments in the detailed topics of this course.
Meanwhile you can read more of Professor Carey's thoughts in the chapter he wrote in a 308 page book published in 2003 titled 'Life Span: Evolutionary, Ecological and Demographic Perspectives". The book is a tour de force of theories and science of life spans of humans and other species.
If you read Professor Carey's paper on Life Span you will have been on a wide ranging journey through species, record maximum lifetimes and extinction as a species. This a stimulating discussion but we are now going to get back to fundamental human demography.
History and literature talks about a human life span conceptually as "three score years and ten" or 70 years. In the developed world of industrial revolution, disease eradication and medical technology, humans are living well beyond this age. As Professor Carey says, you can't say there is a limit to which any individual can live but the probability becomes infinitesimal as you head towards infinity.
For practical purposes of demographic calculations, current Life Tables generally terminate at age 110. Beyond that age data is insufficient to develop reliable average death rates as an indication of an age specific mortality rate. So for projecting populations with age specific mortality rates it is conventionally sufficient to use a life span maximum of 110.
Moving on from the concept Life Span we will now look at the Demographer's statistic, Life Expectancy.
Life Expectancy is the average number of years of life from a particular age onwards, according to the Age Specific Mortality Rates of a Life Table. We will show you how to calculate it shortly.
Usually when people quote Life Expectancy of a population, they really mean Life Expectancy at Birth. They also usually mean the calculation uses a particular calendar year's Age Specific Mortality Rates for all of the ages for that year. Of course looking into the future for a person just born now, there may well be continued improvements in population health that mean people will live longer than implied by the mortality rates at all ages in the current year. There are methods which can be employed to allow for such improvements however we will not add this complexity to the illustration of the life expectancy concept in this course. This issue will be incorporated in population projections covered in the forthcoming 300 Population Dynamics Category of courses.
Let's get the feel of this concept with this simple 3 minute video illustration from INED, the French Institute for Demographic Studies.
Key points from this video are:
Life Expectancy at birth for the population of France in the year 2000 was 79 years. (This is how you state a Life Expectancy calculation.)
It is calculated by:
Starting with a notional group of 1000 live births,
Applying death rates of the year 2000 life table and calculating deaths at each age, and
Calculating the average years lived by the 1000 people - this equals Life Expectancy.
Uses of Life Expectancy Calculation are:
Comparing population mortality of different countries for the same year, and
Comparing different years' population mortality for the same country.
The link below gives you the opportunity to apply what you have learned to calculate life expectancy for Australia for 1971 and 2011. In this Exercise you will learn where to get data from. You might find it useful to print this instruction and record the values suggested - there could be a Quiz on the answers later on.
As we saw in the Exercises above using Australian Life Tables, the life expectancy at birth for Women is longer than for Men. This is a general observation made for large samples of population data in other countries and over past periods. Research is yet to find an explanation for this, other than being a factor of the different DNA of Men and Women and that it may have some evolutionary process behind it. For example it could be a balancing measure for the excess of Males born versus Females so that by the time reproduction ages are reached the sexes are balanced. If you click the link below to these Life Tables, you will find a detailed analysis of the difference between Male and Female life expectancy in section 1.4 from page 11.
Other observations have been made of differences in life expectancy according to income and occupational status. Some differences by occupation would derive from riskiness of occupations. This might also feed into different income levels if safer occupations pay more, particularly where management roles pay higher salaries and the roles involve less risk. Another possibility, particularly in countries without universal health care, is that people with higher incomes may be able to afford to pay for better health care.
The following article describes differences in Life Expectancy in France based on sex and occupation.
In the following 4 minute video, Dr Raj Chetty describes the results of a study of US Life Expectancy according to income level and sex.
You can download Dr Raj Chetty's paper on this topic from the link below.
The main conclusions from this research on the United States between 2001 and 2014, were:
Higher income was associated with greater longevity.
Differences in life expectancy across income groups increased over time.
The association between life expectancy and income varied substantially across geographic areas.
The differences in life expectancy were correlated with health behaviours and local area characteristics.
If you did the Exercise in 205.2 on Australian Life Expectancy in 1974 and 2011, you would have seen the calculation of Life Expectancy at Birth for Women extends by 10 years and for Men by 12 years between 1974 and 2011. The question then arises "Are these extra years lived in blissful healthy retirement or is it longer periods alone in an aged care home?". Retirees would also like to know this in advance so their savings and lifestyle plans can adjust. Governments would also like to know this so Health Care workforce and budgets can adjust.
Valuable research in this field is being done by Professor Carol Jagger and her team at the University of Newcastle in the UK at the Institute for Ageing and Healthy Life Expectancy. Professor Jagger describes the work of the Institute in this 4 minute video produced by AXA, the sponsor of the Institute.
As mentioned by Professor Jagger, old age is including a greater proportion of people with multiple health issues rather than just one condition. Health services will need to adapt from being single specialty focus to whole health focus. Data collection also needs to be developed further to get a more accurate picture of exactly how much extra life span will be lived actively.
The methods of calculating Healthy Life Expectancy (HALE) are much more complex than you saw for Life Expectancy. It is a fairly recent development compared to the long history of life tables using just mortality. The following paper is a neat summary of the HALE methodology and includes results for changes in HALE over 12 years from 2000 to 2012.
The paper by WHO showed that globally, Health Adjusted Life Expectancy at birth in 2012 for males and females combined was 61.7 years, which is 8.6 years lower than total life expectancy at birth. In other words, poor health resulted in a loss of nearly 9 years of healthy life. Results are shown for regions and selected countries within the paper.
A 30 page Paper on Australian Health Adjusted Life Expectancy by the Australian Institute of Health and Welfare can be viewed here:
An interesting graph from the paper shows the percentage of future years lived in Full and ill health, measured from different ages onwards. (See below)