Population — common mistakes

If asked why a developing country's birth rate is high, give three distinct reasons and link each to development — 'infant mortality is high, so…', 'few women are in paid work, so…'. Lists without links score only half the marks.

Any 'effects of an ageing population' question should include a government response — raising the retirement age, encouraging immigration, raising taxes, or encouraging private pensions — and a comment on which groups each response hurts.

Because its population is older. The death rate counts deaths per 1 000 people of all ages, so a country where many people are over 80 records more deaths per 1 000 even though life expectancy is higher.

Neither on its own. What matters is population relative to resources and capital — output per head. The optimum population is the size that makes output per head as high as possible; above it the country is over-populated, below it under-populated.

Immigrants are mostly of working age, so immigration lowers the receiving country's dependency ratio and raises the ratio in the country they leave, where the remaining population is older and younger.