Cambridge O Level Economics: Population (2281) – Revision Notes

Quick recall notes for section 5.3, Population, of the Cambridge O Level Economics (2281) syllabus for examination in 2026, version 2. For full explanations and longer worked examples, read the study guide first. There are no tiers. The syllabus says you must interpret a population pyramid but not draw one. All countries and figures here are invented and illustrative.

Links: practice questions, Cambridge O Level Economics hub, printable checklist, economic development practice set and free diagnostics.

1. Definitions and formulas (5.3.1)

Term	Meaning or formula
Birth rate	live births per 1,000 people (divide by population, multiply by 1,000)
Death rate	deaths per 1,000 people (same method)
Natural change	births − deaths
Immigration	arrivals who settle in the country
Emigration	residents who leave to settle abroad
Net migration	immigrants minus emigrants (may be negative)
Total change	natural change plus net migration
Growth rate (%)	total change ÷ opening population × 100
Natural increase per 1,000	birth rate − death rate (divide by 10 for %)

Method in steps: finding population growth

1. Find the birth rate and death rate per 1,000 if asked.
2. Subtract deaths from births to get natural change.
3. Subtract emigrants from immigrants to get net migration. Keep the sign.
4. Add the two to get total change.
5. Divide by the opening population and multiply by 100.
6. Add total change to the opening figure for the closing population.

Worked reminder (Country W, illustrative)

Opening population 18,000,000. Births 288,000. Deaths 216,000. Immigrants 36,000. Emigrants 18,000.

Birth rate  = 288,000 / 18,000,000 x 1,000 = 16.0 per 1,000
Death rate  = 216,000 / 18,000,000 x 1,000 = 12.0 per 1,000
Natural     = 288,000 - 216,000 = +72,000 (0.4%)
Net migr.   = 36,000 - 18,000   = +18,000
Total       = +90,000 -> 90,000 / 18,000,000 x 100 = 0.5%
Closing     = 18,090,000

2. Why rates differ between countries (5.3.2)

Rate	Pushes it down	Pushes it up
Birth rate	Girls’ education, paid work for women, contraception, falling infant deaths, high child costs in cities, state pensions, later marriage	Weak education for girls, little access to family planning, high infant deaths, children needed for farm work or old-age support, cultural preference for large families, family-friendly policies
Death rate	Better healthcare, vaccination, clean water, sanitation, food supply, higher incomes, peace	War, famine, epidemics, poor sanitation, poverty, and an old age structure

Net migration is a balance. A country has net immigration when pull factors (jobs, higher wages, safety, services, easy entry rules) outweigh the pull of other countries. It has net emigration when push factors (unemployment, low pay, conflict, poor services) are strong at home and attractive options exist abroad.

Key links to remember:

• Death rates usually fall first as healthcare spreads. Birth rates fall later. Growth is fastest in the gap.
• An ageing country can have a high death rate with good healthcare.
• Falling infant mortality lowers the birth rate after a delay, because families no longer need extra children as insurance.

3. Optimum population (5.3.3)

• Optimum population: the size at which output per head is at its peak for the country’s land, resources, capital and technology.
• Under-population: fewer people than the optimum. More workers would raise output per head.
• Over-population: more people than the optimum. Extra workers add less than the average.
• The optimum moves up with better technology, capital and skills, and down when resources are lost.

Worked reminder (Country X, illustrative)

Population (millions)	Total output (billions)	Output per head
2	30	15
4	72	18
6	120	20
8	144	18

Optimum = 6 million (output per head 20). At 8 million the extra 2 million add only 24 billion, which is 12 each, below the average of 20. Country X would be over-populated at 8 million.

4. Effects of population size and structure (5.3.3)

Change	Possible benefits	Possible costs
Rising size	More workers, bigger market, more taxpayers, wider skills	Pressure on land, housing and water; unemployment; more school and hospital spending; lower output per head above the optimum
Falling size	Less resource and environmental pressure; output per head may rise if over-populated	Labour shortages, fewer taxpayers, weaker demand, school closures
Young structure	Large future workforce; growing market for youth goods	Schooling costs; youth unemployment risk
Ageing structure	Experienced workers; demand for care and leisure services	Pension and health costs; fewer taxpayers per pensioner; labour shortages
Gender imbalance	Remittances where one gender migrates for work	Fewer future births if women are few; skills gaps; social strain

Real GDP per head

Growth in GDP per head ≈ GDP growth − population growth. Exact: (1 + g_GDP) ÷ (1 + g_pop) − 1. If GDP grows 5% and population 3%: 1.05 ÷ 1.03 − 1 = 1.94%.

Chain of reasoning for an ageing population

Low birth rate and long life expectancy → more people aged 65 and over, fewer workers → fewer taxpayers per pensioner → government must raise taxes, borrow or cut other spending to pay for pensions and healthcare → possible labour shortages and higher wages → policies such as raising the retirement age or encouraging immigration.

5. Interpreting a pyramid

Steps: (1) width of the base; (2) width of the middle; (3) width of the top; (4) left against right for gender; (5) bulges or dents that suggest migration, past baby booms or past conflict.

Shape	Reading
Wide base, tapering quickly	High birth rate, young, fast growth
Straight sides	Low birth and death rates, stable size
Narrow base, wide top	Low birth rate, ageing, possible fall in population
Bulge of one gender at working ages	Migrant workers of that gender

Dependants per 100 workers (a reading aid that the syllabus does not name) = (aged 0-14 + aged 65 and over) ÷ aged 15-64 × 100. Example: 25% aged 0-14, 9% aged 65 and over, 66% aged 15-64 gives 34 ÷ 66 × 100 = 51.5. Workers per person aged 65 and over = 66 ÷ 9 = 7.3.

Evaluation prompts

Use these to turn a list into a judgement:

• Size against the optimum. Is the country above or below the point where output per head peaks?
• Speed. A slow change gives time to build schools, homes or pension funds. A sudden one does not.
• Skills and productivity. Extra workers help only if they have the skills and capital to be productive.
• Time period. A young population is a cost now and may be a gain in fifteen years.
• Policy. Education, jobs growth, family policy and migration rules can change the outcome.
• Evidence. What do the figures in the question actually show? Use two or three of them.

Quick self-test

1. Define net migration.
2. Births are 50,000 in a population of 2,500,000. Find the birth rate.
3. Birth rate is 20 and death rate is 8 per 1,000. What is the natural increase as a percentage?
4. A country of 4,000,000 has 20,000 immigrants and 32,000 emigrants. Find net migration, and net migration per 1,000.
5. GDP grows 5% and population 3%. What is the growth of GDP per head?
6. GDP grows 3% and population 4%. What happens to GDP per head?
7. Give two reasons a rich country may have a higher death rate than a poorer one.
8. Define optimum population.
9. In the table above, which population is over-populated and why?
10. Give two effects of an ageing population on government spending.
11. Explain how a wide base on a pyramid can lead to unemployment.

Answers

1. Immigration minus emigration.
2. 50,000 ÷ 2,500,000 × 1,000 = 20 per 1,000.
3. 20 − 8 = 12 per 1,000 = 1.2%.
4. 20,000 − 32,000 = −12,000, which is −3 per 1,000 (net emigration).
5. 1.05 ÷ 1.03 − 1 = 1.94%.
6. 1.03 ÷ 1.04 − 1 = −0.96%, so it falls.
7. A larger share of elderly people; more deaths from age-related illness, even with good healthcare.
8. The population with the highest output per head, given resources, capital and technology.
9. 8 million: output per head falls to 18 and each extra person adds less than the average.
10. Higher pensions and higher healthcare spending.
11. Many children become workers together; if jobs grow more slowly than the labour force, unemployment rises.

Where marks are usually lost

• Giving a rate per person instead of per 1,000, or dropping the sign on negative net migration.
• Forgetting to include migration in total growth.
• Defining optimum population as the largest or the richest, not the highest output per head.
• Saying a high death rate means poor healthcare without checking age structure.
• Describing a pyramid without comparing the base, middle and top.
• Listing effects without a chain of reasoning to workers, taxes, spending or living standards.
• Giving only benefits or only costs when the question asks for evaluation.
• Treating population growth as always bad or always good. It depends on the starting point relative to the optimum.

Official syllabus

Cambridge O Level Economics (2281) syllabus for examination in 2026, version 2, published by Cambridge University Press and Assessment (Cambridge International Education). Section 5.3: Population.