Unit 4: Human Population - Trends, Structure and Change
Core concepts
Unit 4 investigates population size, distribution, composition and change. You must understand the demographic transition model, population pyramids, birth and death rates, natural increase, net migration, fertility and mortality measures, and dependency ratios. Know how to calculate and interpret rates, including crude birth rate, crude death rate, infant mortality rate, total fertility rate and rate of natural increase (births minus deaths per 1,000 people). Understand population momentum and the difference between population growth and population ageing. Be familiar with concepts of carrying capacity, overpopulation and underpopulation, and with migration push-pull factors.
Traps in questions
Students often mix up rate of natural increase with growth rate (which includes net migration). Another trap is reading population pyramids literally - the width of a bar shows numbers in that cohort, not the proportion of the total. When comparing countries, avoid assuming a high total fertility rate always means high population growth; mortality and migration matter. Questions asking for 'reasons for an ageing population' require both falling fertility and rising life expectancy.
Worked example
If a country has a birth rate of 18 per 1,000, a death rate of 7 per 1,000 and net migration of −2 per 1,000, the rate of natural increase is 11 per 1,000 (1.1%), but the overall growth rate is 9 per 1,000 (0.9%) because migration is negative. Always state units.
Rule of thumb
For any population data question: identify the measure, check the units, calculate carefully, then interpret what the figure means for population structure or policy.