Introduction to population structure
The composition of a population according to age groups and gender is known as the age-sex structure. It can be represented by mean of a population pyramid.
The vertical axis of a population pyramid has the population in both age bands of 5 years and the horizontal axis shows the number or percentage of males and females. The pyamid shows longevity in its height. Population pyramids can show:
- the result of births minus deaths in specific age groups
- the effects of migration
- the effects of events such as, war, famine and disease
- an indication of the overall life expectancy of the country.
Age structure can also be measured by a number of indices:
- the dependency ratio
- the support ratio
- the juvenility index
- the old-age index
The dependency ratio shows the relationship between the economically active (working) populatio and the non-economically active (dependent) population. In the EU, the dependent population is those people aged under 19 and over 60. The dependency ratio can therefore be calculated by:
dependency ratio = (population 0-19)+(population over 60) / population 20-59
The higher the dependency ratio, the more the non-economically active proportion is dependent on the working population.
The support ratio is the inverse of the dependency ratio. The juvenility index is calculated by: juvenility index= population 0-19 / population 20 and over
The higher the juvenility index, the greater the proportion of younger people in a population.
The old age index is calculated by: old age index= population 60 and over / population 20-59
The higher the old age index, the greater the proportion of elderly people in a population.
The changing age-sex structure of the UK
The population pyramid for the UK for 2001 shows a relatively smooth pyramidal shape, with some slight buldges and indentations. These slight variations can be explained by the circumstances at the time each age group was born and by later factors affecting that group.
The buldge of people in thier 30s demonstrates that the birth rate was slightly higher in the 1960's and 1970's. There may be two reasons for this. First, in the 1960s was a period of rising national prosperity and increasing personal income. In the 'swinging sixties', there was lessening of sexual taboos and an increase in freedom for women. Second, this was the time at which people who themselves had been born in a baby boom following the Second World War was entering their fertile years. As there were more fertile indiviuals, more babies were born. Most people who were parents in the 1960s were in thier 50s in 2001, and feature as a slight bulge on the pyramid. These examples demonastrate that population growth is cyclical and that to some extent changes can be predicted, so long as social norms are retained.
The changing age-sex structure of the UK - 2
Two further points illustrate the changing nature of a population structure. In the 2001 pyramid, there is a relatively large number of people over the age of 80. The reasons for this are complicated. People born in the period 1910-20 were often part of large families. This was both traditional and functional. Many young children died in infancy from infectious diseases and a large family acted both as a source of income and as a form of sercurity in old age. As the century progressed, however, death rates fell. Improvements in medical care and the development of new drugs and treatments have meant that some of these people, particulary women, are living into their 80s and 90s.
The second point concerns the younger part of the pyramid. As mentioned above, there was an increase in birth rates in the 60s. The people born then became fertile in the 1980s and 1990s, so a cycical increase in birth rates would be expected at that time. This has not happened to the extent predicted because social norms have changed.
The changing age-sex structure of the UK - 3
In recent decades, young adults have been less willing to have children. There are various reasons fir this: the increased availabilty of contraception, abortion and sterilization; the growing importance of material possessions; and the disire for women to have careers. With hindsight, it is possible to add another factor. The economic recession of the late 1980s and early 1990s left many young adults feeling financial insercure. A lot of women were forced to become the main breadwinners as male employment in mining and manufacturing fell.
The net results is that the early part of the 21st century, the UK has an ageing population. The proportion of the population aged 50 and over has increased significantly since the start of the 20th cenrtury. There has also beena risk in the 'very elderly' - people aged 80+. Population projections suggest that by 2021 there will be more than 2 million people over 80 - 5% of the population. At the same time the number of people aged 16 and under has been falling prgressively. It is anticipated that before the next cencus in 2011, the number of people aged 65+ will exceed those under 16 for the first time.
Links between the DTM and age-sex structure
The demographic transition model can be used to demonstrate changes in age-sex structure both spatially and over time. This can be seen in teh characteristics shapes and names of the pyramids at each stage of the DTM.
- Stage 1 - high fluctuating - high birth rate; rapid fall in each upward age group due to high death rate; short life expectancy.
- Stage 2 - early expanding - high birth rate; fall in death rate so more middle aged people alive; slighlty longer life expectancy.
- Stage 3 - late expanding - declining birth rate; low death rate; more people living to an older age.
- Stage 4 - low fluctuating - low birth rate; low death rate; higher dependency ratio; longer life expectancy.
An ageing population
The population of the world is ageing significantly. In 2005, 10% of the population was over the age of 50. In the developing world this was 8% of the population, and in the developed world 20%. This proportion is expected to increase to 20% by 2050. In 2005. 670 million people were aged 60 years and over. This is projected to increase to 1 billion by 2020 and to 2 billion by 2050. This rise in the median age of the population is caused by increased life expectancy (greater longevity) and the decline in fertility. It is called demographic ageing. Demographic ageing has been a concern for the developed world for some time it is now also beginning to alarm some countries of the developing world. Although ageing of the population has begun later in the less economically developed world, it is progressively at a faster rate than in the developed world. This is because the relative rates of decline in both fertility and mortality are much greater in developing than un developed countries.
The following demographic ageing features have been highlighted by the UN:
- The global average for life expectancy increased from 46 years in 1950 to 64 in 2000. It is projected to reach 74 years by 2050.
- The global median age for males was 26 in 2000 and is projected to rise to 35 years by 2050.
Demographic features that have been highlighted by
- In the less economically developed world, the population aged 60+ is expected to quadruple between 2000 and 2050. The proportion of this population is projected to increase from 8% in 2000 to 22% by 2050 - to a total of 1.9 billion.
- During the same time period, the proportion of children aged sixteen and under is projected to fall from 33% to 20%.
- The population aged 80+ numbered 72 million in 2005. This is the fastest growing section (4.2% annually) of global population and is projected to increase to 394 million by 2050.
- Europe is the 'oldest' region in the world. Those aged 60+ in 2000 formed 20% of the population and this is projected to rise to 35% by 2050.
- Africa is the 'youngest' region in the world. Those aged 15 and under accounted for 42% of the population in 2000. This is expected to decline to 24% by 2050.
- The percentage of old people and thier rate of increase varies among countries. In 2005, those aged 60+ ranged from more than 25% in Japan, Italy and Germany to less than 5% in most tropical African countries in the oil-rich countries of the middle east that attract young workers. By 2050, the range is expected to be even wider, from more than 40% in Japan, Italy. Slovenia and North Korea to even less than 5% in African countries of Equatorial Guinea, Swaziland and Liberia.
Demographic features that have been highlighted by
- The 'oldest-old' age group (80+), will make up over 100 million (in India) and 50 million (in China) by 2050, and more than 15% of the populations of Italy and Japan will be this age.
- In 2005, globally there were 10% more women than men aged 60+, twice as many aged 80+ and four times as many centenarians.
Demographic ageing posses problems for the world as a whole. However it is the less economically developed world that faces the greatest challenage because:
- financial, health and housing resources are inadequate to meet the increasing demands of the elderly.
- traditional support mechanisms for old people are deteriorating in an era of rapid social change.
- the significant decline in fertility is leaving fewer children to care for the elderly parents. In China, 24% of the population will be 65+ by 2050. The first one-child generation will have to care for two parents, and upto four granparents, without siblings to help - the '4:2:1' problem. It will be made worse by the shortage of females, the traditional carers.
Demographic features that have been highlighted by
However, adjustments will also be needed in the more economically developed world. In the EUm it has been predicted that by 2025:
- there will be an increase in the number of people aged 60+, a further 37 million.
- one-third of its population will be pensioners - 111 million people.
- the working population (aged 20-59) will shrink by 13 million.
- the numbers of over 60s will outnumber the number of under 20s, for the first time in recorded history.
- there will be three times as many over 80s as there were in 2003.
- there will be 9 million fewer children and teenagers - a 10% decline.
The impact of migration on population structure
Migration affects the population structure of both the area of origin and the area of destination. Impacts on the area of origin include:
- the younger adult age groups (20-34) migrate, leaving behind an older population.
- males are more likely to migrate, causing an indentation on that side of the population pyramid.
- birth rates fall and death rates rise.
Barra, an island in the Outer Hebrides (Scotland), has long experienced depopulation as a result of the poor economic prospects in this remote location. Impacts on the area of destination area that:
- the proportion of younger adult age groups increase.
- males are more likely to migrate, causing an expansion on that side of the pyramid.
- birth rates rise and death rates fall.
Dar-es-Salaam, the largest city in Tanzania, in a thriving international port and has long been a magnet for those seeking employment in that area of East Africa.