Population Pyramids |
Think about it! Try this gap fill exercise |
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A
population pyramid is a graph that allows us to see the gender and
age
structure
of a
population.
There are different shapes to
the pyramids which tell us different things about the population of the
country.
It is often useful to divide population pyramids into
3 distinct age groups or COHORTS- 0-15 or the Young, 16-65 or the
working age and 65+ as the retired sectors of the population.
Knowing the percentage of people in these sectors can allow us to
calculate a Dependency Ratio. This
is the ratio between those of working age and those of non-working age.
The no-working age are known as DEPENDENTS because they depend upon the
working age people to provide for their needs.
This is calculated as:
The ratio for an MEDC usually lies between 0.5 and 0.75. The ratio for an
LEDC is typically higher. Mexico, with a youthful population structure,
has a dependency ratio of 1.04. The higher ratio, the greater the number
of dependents that have to be provided for from the taxes on the
workforce. A ratio of 1 means that for every working age person there is
one dependent person. The UK
had a ratio of 0.49 in 2010 (CIA
FACTBOOK) meaning that for every young or old dependent person there
were approximately 2 working age people.
Stage 1 – LDCs (Least Developed Countries) that are High Fluctuating
These countries have a concave profile because they have high birth rates
and high death rates, plus low life expectancies.
Very few people survive to old age (the average life expectancy
in Sudan was 52 years in 2010) and birth rates are very high.
This cause the population at the base to be prominent and grow
through momentum every year, but these groups are compensated by
Stage 2 – LEDCs that are RAPIDLY GROWING
LEDCs have a triangular shaped pyramid. They have lots of children and
people do not tend to live for a long time (low Life expectancy). These
countries populations grow rapidly as many more children are added to
the population than people die. The Philippines pyramid shows this
perfectly and has a population growing at 1.93% per year.
This does not sound like a big percentage. However, when you do
the math, 1.93% of the 99.99million people that live in the Philippines
means that the population should grow by 1.9 million people!
These are typical of countries at STAGE 2 of the Demographic
Transition Model and have HIGH DEPENDENCY
Stage 4 – MEDCs with STABLE POPULATIONS
Most
MEDCs have a space rocket
shape, with old people living for a long time (high life expectancy),
lots of workers and reasonable numbers of children. These populations
are stable and
are
growing slowly
as the number of young is
just above
the number of people dying. Some MEDCs actually have declining populations where there are not enough children being born each year to replace those dying. Germany is experiencing a period of negative growth (-0.1%). As negative growth in a country continues, the population is reduced. A population can shrink due to a low birth rate and a stable death rate. Increased emigration may also be a contributor to a declining population. Below you can see how these pyramids relate to the Demographic Transition Model |
A population pyramid typical of stage 1 - note the wide base, low life expectancy and concave profile |
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A population pyramid typical of stage 2 - note the wide base, lengthening life expectancy and pyramidal profile |
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A population pyramid typical of stage 3 - note the narrowing base, increasing life expectancy and rocket shaped profile |
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A population pyramid typical of stage 4 - note the narrowing base, long life expectancy and vase shaped profile |
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A population pyramid typical of stage 5 - note the ever diminishing base and very long life expectancies |
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