Population size, growth, structure and migration: WASSCE Economics

Sierra Leone's 2015 census counted about 7.1 million people, and the number keeps rising. How many of them are children? How many live in towns? How fast is the population growing? The answers shape everything from the number of schools needed to the number of jobs the economy must create.

Learning objectives

By the end of this lesson you should be able to:

explain what a census is, its uses and the problems of taking one
calculate birth rate, death rate, natural increase and the growth rate of a population
describe the age, sex, occupational and geographical structure of a population
draw and interpret a population pyramid and calculate a dependency ratio
explain the causes and effects of rural–urban migration

Counting the population: the census

Definition

A population census is an official count of all the people in a country at a particular time, recording details such as age, sex, occupation, education and place of residence.

Sierra Leone took censuses in 2004 and 2015, and Statistics Sierra Leone (Stats SL) carried out a mid-term census in 2021.

Uses of a census: planning schools, hospitals, housing and roads; estimating the labour force; sharing government funds between districts; drawing electoral boundaries; projecting future needs; helping firms find markets.

Problems of taking a census in West Africa: high cost; illiteracy and false information (for example about age); poor roads to remote villages; mobile populations; political interference when counts affect seats or funds; lack of trained enumerators; distrust of officials.

How populations grow

A population changes through births, deaths and migration.

Definition

Crude birth rate: live births per 1,000 people in a year.
Crude death rate: deaths per 1,000 people in a year.
Natural increase: birth rate minus death rate.
Net migration: immigrants minus emigrants.

\text{birth rate} = \dfrac{\text{live births}}{\text{population}} \times 1000

\begin{aligned}&\text{birth rate} \\ &= \dfrac{\text{live births}}{\text{population}} \times 1000\end{aligned}

Worked example

A district has a population of 400,000. In one year there are 14,000 births, 5,200 deaths, 1,000 immigrants and 3,000 emigrants.

Birth rate $= \dfrac{14000}{400000} \times 1000 = 35$ per 1,000
Death rate $= \dfrac{5200}{400000} \times 1000 = 13$ per 1,000
Natural increase $= 35 - 13 = 22$ per 1,000, that is 2.2%
Net migration $= 1000 - 3000 = -2000$ (a net outflow)
Total change $= 14000 - 5200 - 2000 = 6800$ people
Growth rate $= \dfrac{6800}{400000} \times 100 = 1.7\%$

Why birth rates are high in West Africa: early marriage; the value placed on large families; children as farm workers and as support in old age; high infant mortality (parents have more children expecting some to die); limited use of family planning; religious and cultural beliefs.

Why death rates have fallen: better medical care and vaccination; cleaner water and sanitation; better nutrition; health education.

Population structure

Age structure and the population pyramid

A population pyramid shows the share of males and females in each age group.

Two population pyramids: a young population with a very wide base of children narrowing quickly with age, and an ageing population with narrow young age groups and many people in middle and old age

Figure 1. A young population such as Sierra Leone's (left) and an ageing population (right). Illustrative shapes. WASSCE Tutor diagram.

A broad base shows a high birth rate and many children; a narrow top shows that few people live to old age. This is typical of Sierra Leone and most of West Africa, where over 40% of people are under 15.

The dependency ratio

Definition

The dependency ratio compares the number of dependants (people under 15 and over 64) with the number of people of working age (15–64).

\text{dependency ratio} = \dfrac{\text{under 15} + \text{over 64}}{\text{aged 15 to 64}} \times 100

\begin{aligned}&\text{dependency ratio} \\ &= \dfrac{\text{under 15} + \text{over 64}}{\text{aged 15 to 64}} \times 100\end{aligned}

Worked example

A town has 42,000 people under 15, 4,000 over 64 and 54,000 aged 15–64.

\text{dependency ratio} = \dfrac{42000 + 4000}{54000} \times 100 \approx 85

\begin{aligned}&\text{dependency ratio} \\ &= \dfrac{42000 + 4000}{54000} \times 100 \\ &\approx 85\end{aligned}

Every 100 people of working age support about 85 dependants. A high ratio means heavy spending on schools and health, and less income left to save.

Sex, occupational and geographical structure

Sex structure: the balance of males and females, often given as the number of males per 100 females (the sex ratio).
Occupational structure: how workers are divided between primary, secondary and tertiary production. In Sierra Leone most people still work in agriculture; richer countries have most workers in services.
Geographical distribution: where people live. Population is dense in Freetown and the Western Area and in mining and trading towns, and sparser in parts of the provinces.

Rural–urban migration

Many young people move from villages to towns, especially to Freetown.

Causes (pull and push factors): better job prospects and higher wages in towns; schools, hospitals, electricity and water; bright lights and entertainment; poverty, low farm incomes and lack of amenities in villages; land disputes; escape from traditional obligations.

Effects:

On towns	On rural areas
Overcrowding, slums and pressure on housing	Shortage of young farm workers
Unemployment and crime	Falling food output
Strain on water, power, schools and transport	Ageing population left behind
A larger pool of labour for industry	Remittances sent home by migrants

Remedies: develop rural amenities (roads, schools, clinics, electricity); support farming with credit and better prices; locate industries in provincial towns; encourage agro-processing in rural areas.

Key points

A census counts the population; it guides planning but is costly and hard to carry out.
Population changes through births, deaths and migration; rates are per 1,000 people.
Sierra Leone has a young population: a broad-based pyramid and a high dependency ratio.
Rural–urban migration brings labour to towns but also slums, unemployment and labour shortages on farms.

WASSCE examination focus

WAEC tests this

Expect to state the uses and problems of a census, to calculate birth rate, death rate, natural increase or the dependency ratio, to explain the shape of a population pyramid, and to discuss the causes and effects of rural–urban migration and its remedies. Show the formula, substitute the figures and give the unit (per 1,000, or %).

Quick check

A country of 8 million has 280,000 births in a year. What is its crude birth rate?
What does a broad base on a population pyramid show?
Give two reasons why young people move to Freetown.
Calculate the dependency ratio if there are 30,000 dependants and 50,000 people of working age.

Answers: 1. $\dfrac{280000}{8000000} \times 1000 = 35$ per 1,000. 2. A high birth rate and a large number of children. 3. Any two: better jobs and wages, schools and hospitals, electricity and water, entertainment, poverty in villages. 4. $\dfrac{30000}{50000} \times 100 = 60$ .

Population size, growth, structure and migration

Learning objectives

Counting the population: the census

How populations grow

Population structure

Age structure and the population pyramid

The dependency ratio

Sex, occupational and geographical structure

Rural–urban migration

Key points

WASSCE examination focus

Quick check

Keep going with population

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