Brief Description

How many people are there in the world, and how rapidly is the population growing? Starting with population data from 1650 to the present day, projections are made for the future, and some of the implications discussed. Subsequent sections illustrate the demographic techniques of population pyramids and birth and death rates as thev affect growth.

Design time: 4 hours

Aims and Objectives

On completion of this unit pupils should be able to draw, read and interpret population pyramids, make simple projections from graphs and tables and calculate and use crude birth rates and crude death rates. They will have practised interpreting simple tables, plotting time series, questioning assumptions, drawing inferences, identifying modal groups and drawing time charts. They will be more aware of the problems of collecting data and obtaining accurate census figures, and of the implications of birth and death rates to future population trends.

Prerequisites

Pupils should be able to plot points on a graph, Join them with a smooth curve and extrapolate, and draw bar charts. They should also be familiar with percentages.

Equipment and Planning

A calculator,would be useful for Sections C and D. Graph paper is needed for Section B, Pages R1 to R3 contain partly completed tables and graphs.

Section A begins with a discussion on the meaning of overpopulation and moves on to looking at the actual data and making predictions for the future. Section B introduces population pyramids to make points about the implications of age distribution within the population. It looks initially at a town where there are many retired people and compares this with a new town. It then moves on to looking at some figures for continents.

Section C introduces the crude birth rate and crude death rate, and Section D is a simulation showing the effect of birth and death rates on a fictitious population of rats.

Detailed Notes

Section A

A1
Overpopulation is not a simple idea. Discussion may centre on, for example, whether it means that there are a lot of people, there is a high population density or the country is not self-sufficient in food. Countries that may be mentioned as having overpopulation problems include India, Pakistan, Indonesia, Latin America and some African countries.

A2
These stick diagrams also show the increase by crowding more stick men in the same size circle. This is followed up in Section A5. The population figures are quoted to the nearest hundred million. If more accurate figures are required than those, Table T1 can be used.

Table T1 - World populition figures

A3
Without the 1975 data the other points seem to lie on a reasonable curve. The 1975 figures show, a dramatic rise over the previous 25 years, and it is not easy to draw a reasonable curve to project through to the year 2000 AD). This serves to emphasize the difficulty of making such projections and the amount of legitimate variability that there may be in these estimates. A straight line extension of the curve can lead to a gross underestimate.

A4
The accuracy of a projection depends on the accuracy of the initial data and on the validity of the underlying assumptions. It is not easy to get even the initial population figures accurately as will he realized by considering the practical difficulties involved.

An example of 'Inaccuracy' in population estimates occurred recently when a certain developing country was required to give an estimate of its present population to two different international organizations. One estimate was to be used as a basis for the allocation of aid to that country, while the other was to determine its liability to an African Economic Community of which it was a member. The two estimates differed by some 30%! (See also Reference 1, for a general discussion.)

Past estimates are not as likely to be as accurate as present estimates, since, with the growth of civilization and communications, it is now easier to keep track of everybody. Some of the problems of doing this are covered in the unit Sampling the Census.

Present trends may well not continue into the future; indeed in the long term they cannot, as is brought out in the next section. The illustrations are of earthquake, storm, flood, atomic war, drought and scientific discoveries. The last could work in two ways. By improving medical care death rates can be lowered; by developing safe methods of contraception birth rates can be lowered. One major factor not illustrated is famine due to food shortage.

A5
Overpopulation leads to overcrowding. The decrease in the number of hectares (Including desert) available per person from 1650 to 1975 Is dramatic, and shows the gain in food supplies due to improved agriculture techniques. Figure 7 on page R1 is needed for this section. The section leading to c and f makes most forcefully the point that things cannot go on as they are, but this has been made optional.because many pupils are put off by the large numbers involved.

A6
This section summarizes the main lesson of Section A.

Section B

B1
The 'picture' of the population pyramid (Figure 2) should he clear enough for most pupils but may need explaining to some. It can be described as two horizontal histograms side by side sharing the same vertical axis. The questions concentrate mainly on reading the population pyramid. The accurate figures are given in Table T2.

Table T2 - Population (in thousands) of Worthing, 1971

The figures for Worthing and for England and Wales (Table 3) are given as actual numbers rather than as the proportions or percentages used later.

In j it is hoped that pupils will spot the large number of older women and the disproportionate number of old people altogether. They may need some explanation about Worthing being a place where people retire to. Question n raises some of the social implications of having a population which has a large proportion of retired people. How, do amenities get paid for?

The age groups have each been given as a range of 15 years (so that 75+ has been interpreted as 75 to 89). This means that the bars of the histogram in the pyramid are all the same width, and populations can be read off from the lengths of the bars.

B2
In contrast with Worthing, Skelmersdale is a new town with a lot of young people. This is hinted at in a and followed up in the comparative questions on the population pyramids. These pyramids are plotted using percentages so that the overall area of each is the same and the comparison can be made more easily. The large number of young people in Skelmersdale leads us to expect higher population growth in h.

B3
The developing country pyramid is number (iii), and hence in Figure 5 it is poptilation pyramid number 1 which is of Africa. In the other pyramids the effect of war is seen on the 50-54 age group and their children in the 25-29 This is more pronounced in population pyramid number 4, so this is of USSR and number 3 is of Western Europe. It may be interesting also to discuss the shape of the population pyramid of North America.

B4
Population pyramids only give ages. not occupations. Problems in d may concentrate on population growth. in Africa, large numbers of young dependents in Africa, old dependents in North America, few children in USSR leading to a lower working population later, etc.

Section C

This section is simply the definition and application of two formulae. If division is a problem, then a calculator may save considerable time. These measures are termed 'crude' in that they relate births deaths to the whole population. They are not in any way 'age-specific'.

C1
Instead of the crude birth rate, the number of births is often measured against the number of women of child-bearing age. The last four calculations of b indicate how the birth rate has changed in the UK during this century. The effect of even small changes on population projections can be seen in the projections Published by the Office of Population Censuses and Surveys.

C2
The crude death rate can he made less crude by analysing it within particular age groups. The crude death rate seems to show Worthing as an unhealthy place. but it is mainly due,to the large number of elderly people living there. The explanation of d is that the population grew during the same period.

Section D

The simulations suggested here are deterministic, but do give some indicaition of the effect of births and deaths. Figure 8 and Table 6 from page R2 are required for this section.

D1
Notice that it is one-fifth of the rats whlch die at the end of years 0-1 and 1-2. The key to the size of the next generation lies with the number of fertile (one year old) females in the present year. Notice that, although every one year old female has two offspring and so it might be thought that the population would replace itself, the race still becomes extinct because of the deaths occurring at the end of the first year of life. A similar argument shows why the rule 'every woman has exactly two children' would not lead to a stable human population.

D2
Although this is optional there is much scope here for experimenting with different initial populations, and different rules for birth and death. The effect of these on the eventual population can then be seen. Table T3 gives some suggestions. Different pupils might try different rules and compare their results. If a computer is available, the scope for invention of rules is even greater: more generations, different proportions of male to female, etc.

Table T3 - Some suggested simulations for D2

Simulation 1 can be compared with D1. It shows the effect of increasing the birth rate while the death rate remains constant. The population grows Simulations 2 and 3 are both stable, but whereas the population of simulation 2 remains constant at 600 that of simulation 3 rises from 600 to oscillate between 850 and 950. This shows the delayed effect of the large number of young rats and can he compared with the problems of, say, Africa where cutting the birth rate would similarly have a delaved effect before the population stabilised. Simulation 4 can be compared with simulations 2 and 3. and it shows how, a rise in birth rate can lead to the population getting out of hand. Simulation 5 is a stable population with a high birth rate and a high death rate.

References

1. On the Accuracy of Economic Observation by 0. Morgenstern, Revised edition (Princeton University, 1963)
2. Population and Environment (Longman and Penguin for the Schools Council General Studies Project, 1972)
3. The Population Explosion - an Interdisciplinary Approach, Units 32-36 of the Open University's 'Understanding Society: A Social Science Foundation Course' (Open University Press, 1972)

Answers

Page R1

Figure 6- World population

Figure 7 - Amount of land per person

Page R2

Figure 8 - Population pyramid, England and Wales, 1975

Table 6 - Number of dirty rats each year

Page R3

Figure 9

Test Questions

1. If you are given a graph of world population over the last 100 years, how can you make a projection of future populations?
2. A population pyramid shows the proportion of men and women at different ages. Why is it usually wider at the bottom than at the top?
3. Developing countries usually have population pyramids with very wide bases. What does this tell us?
4. Draw a population pyramid from the following data for England and Wales (1951).
   

   Age	Men(%)	Women(%)
   0-14	11	11
   15-29	10	10
   30-44	11	11
   45-59	9	11
   60+	7	9
   	48	52

5. In a town or country we can measure 'the number of deaths in a year for every 1000 people in the population'. What is this measure called?
6. What is a crude birth rate? What do we use this for?
7. In a town whose population was 23000 during a certain year, the numner of deaths was 210 and the number of births was 400. Calculate (i) the crude death rate, and (ii) the crude birth rate.

Answers

1		Draw a smooth curve through the points and extend it.
2		These are usually more children than adults.
3		A very large proportion of the population is children; there is a high birth rate and a high death rate.
5		Crude death rate.
6		Number of births in the year x 1000 Year population To estimate future population figures
7	(i)	210/23 9.1
	(ii)	400/23 17.4

Connections with Other Published Units from the Project

Other Units at the Same Level (Level 3)

Car Careers
Net Catch
Cutting it Fine
Phoney, Figures
Pupil Poll

Units at Other Levels in the Same or Allied Areas of the Curriculum

Ievel 1

If at first ...
Lelsure for Pleasure

Level 2

Authors Anonvrrous
Seeing is Believing
Getting it Right

Level 4

Figuring The Future
Sampling the Census
Smoking and Health
Retail Price Index

This unit is particularly relevant to: Humanities, Social Science, Integrated Science, Mathematics.

Interconnections between Concepts and Techniques Used in these Units

These are detailed in the following table. The code number in the left-hand column refers to the items spelled out in more detail in Chapter 5 of Teaching Statistics 11-16.

An item mentioned under Statistical Prerequisites needs to be covered before this unit is taught. Units which introduce this idea or technique are listed alongside.

An item mentioned under Idea or Techniques Used is not specifically introduced or necessarily pointed out as such in the unit. There may be one or more specfic examples of a more general concept. No previous experience is necessary with these items before teaching the unit, but more practice can be obtained before or afterwards by using the other units listed in the two columns alongside.

An item mentioned under Idea or Technique Inroduced occurs specifically in the unit ind, if a technique, there will be specific detailed instruction for carrying it out. Further practice and reinforcement can be carried out by using the other units listed alongside.

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