What makes a population change
Population changes two ways. Natural change = birth rate − death rate, both measured per 1,000 of the population per year. Net migration = immigration (people entering) − emigration (people leaving). The population grows when births plus immigration exceed deaths plus emigration. Work the two components separately, then combine them.
Why growth rates differ between countries
Many low-income countries grow fast: high birth rates (limited contraception, children seen as income or old-age support, high infant mortality) and falling death rates (better healthcare, sanitation, food). Many high-income countries grow slowly or shrink: low birth rates (cost of children, women in careers, family planning) and an ageing population. In the exam, explain why — do not just state that rates differ.
Optimum, over- and under-population
The optimum population gives the highest output per head (best average living standards) for a country's resources and technology. Over-population: too many people for the resources, so output per head would rise if the population fell. Under-population: too few people to use resources fully, so output per head would rise if it grew. These compare people relative to resources, not the absolute number.
Drawn from real examiner reports.
Immigration ≠ emigration
These are opposites. Immigration = people moving into a country; emigration = people moving out. Net migration = immigration − emigration. A frequent error is to swap them, or to treat people moving within a country (countryside to city) as migration into or out of it, which it is not.
June 2023 Paper 22 Q4(a): candidates confused immigration (entering a country) with emigration (leaving), and others confused immigration with movements from one part of a country to another.
Population size does not set the rate
Birth and death rates are measured per 1,000 of the population, so they are ratios, not totals. A bigger population does not by itself raise the death rate — what matters is healthcare, conflict, diet and the average age. Give a genuine cause, not "the population is large".
June 2023 Paper 12 Q3(a): a common error when giving reasons death rates vary between countries was to state the size of the population, but because death rate is per 1,000 this makes no difference to the rate — though the average age would.
Labour force ≠ people employed
The labour force (working population) is everyone willing and able to work — the employed plus the unemployed seeking work. So an unemployed person finding a job does not enlarge it; they were already counted. The labour force grows via a higher birth rate (long run), net immigration of working-age people, a higher retirement age or a lower school-leaving age.
June 2023 Paper 12 Q3(b): the least successful answers gave causes that do not change the size of the labour force — such as a previously unemployed person getting a job — confusing the labour force with those in employment. November 2022 Paper 22 (b) made the same point about the quantity of labour.
Divide by 1,000, not 100
To find the number of births or deaths, multiply the population by the rate and divide by 1,000 — not 100. For a birth rate of 10.2 per 1,000 and population 1.2 m: 1.2 m × 10.2 ÷ 1,000 = 12,240. Dividing by 100 makes the answer ten times too big; multiplying by 1,000 is also wrong.
June 2022 Paper 22 Q1(a): in a birth-rate calculation (births = population × rate ÷ 1,000), common errors divided by 100 not 1,000, or multiplied the rate by 1,000.
Use the right figure in a calculation
In a population calculation, read the numbers carefully. Use the actual population, not another figure such as the optimum population, and keep the decimal place. Examiners saw candidates take a percentage of the wrong total, or slip a decimal (27,650 instead of 276,500). Check which figure the question asks you to use.
June 2023 Paper 22 Q1(a): working out 35% of the population for the labour force, a few candidates wrongly used the optimum population figure (1,100,000) or slipped a decimal (27,650 instead of 276,500).
Dependants: children and pensioners
The dependency ratio compares dependants — children below working age and people above retirement age — with the working population. So a low birth rate lowers the ratio (fewer child dependants) while an ageing population raises it (more pensioners). Do not treat every population change as moving the ratio one way.
June 2022 Paper 22 Q3(d): on the effects of a very low birth rate, strong answers noted the lower dependency ratio as well as the smaller, older labour force.
The Paper 2 (a)–(d) ladder
The 0455 Paper 2 ladder: (a) define (2) — precise meaning only; (b) explain (4) — one point developed; (c) analyse (6) — a sustained one-sided chain, no evaluation; (d) discuss (8) — both sides plus a supported judgement.
Judge a (d) with optimum population
On "does a bigger population benefit the economy?", weigh a larger labour force and tax revenue against over-population straining services. Judge with the optimum population: below it, growth helps; above it, growth harms.
Explain why rates differ
Do not just state that birth or death rates differ — give a cause (family planning, healthcare, migration) and a consequence (faster or slower growth). Every population point should carry a reason, not a bare comparison.
Show working in population sums
For per-1,000 calculations, set out the steps: number = population × rate ÷ 1,000. Showing the working earns method marks even if the final figure slips, and helps you avoid the divide-by-100 trap.
A country's population changes through two channels:
Self-check — don't mix these up: immigration is into the country, emigration is out of it. People moving from the countryside to a city is internal movement and is not migration into or out of the country.
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