Births minus deaths: The natural increase rate shows how fast a population grows from births and deaths alone. It uses the crude birth rate and the crude death rate.
The points to remember
- Natural increase = births − deaths: it leaves out migration.
- As a rate: NIR = CBR − CDR, given per 1000 people.
- As a percentage: NIR (%) = (CBR − CDR) ÷ 10.
- From totals: (births − deaths) ÷ population × 100 gives the same %.
- NIR can be negative: a natural decrease, when deaths outnumber births.
- Always write the unit: % or per 1000. A bare '0.8' is not an answer.
Worked example: two ways to the same answer: From the rates: NIR = (CBR − CDR) ÷ 10 = (5.7 − 13.3) ÷ 10 = −0.76% (or −7.6 per 1000).
From the totals: (686,061 − 1,605,298) ÷ 120,300,000 × 100 = −919,237 ÷ 120,300,000 × 100 = −0.76%.
Real example: Japan's natural decrease of 919,237 people in 2024 is like losing a city the size of Naples in one year.
Remember it as: Births minus deaths, divide by ten, add the % sign.
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A growth rate of 2% sounds small, but it doubles a population quickly. The doubling time turns a percentage into years, using the rule of 70.
Doubling time
- Doubling time = the number of years a population takes to double at its current growth rate.
- Rule of 70: doubling time = 70 ÷ growth rate (%).
- Use the growth rate as a %: if the NIR is given per 1000, divide by 10 first.
- If only birth and death rates are given, work out the NIR first: (CBR − CDR) ÷ 10.
- Faster growth = shorter doubling time. A shrinking population never doubles.
- Give the unit: years.
Worked example: Niger grows by about 3.3% a year.
DT = 70 ÷ growth rate = 70 ÷ 3.3 = 21 years. At that rate Niger's population doubles in about 21 years.
From birth and death rates: a country with CBR 16.17 and CDR 6.28 has NIR = (16.17 − 6.28) ÷ 10 = 0.989%, so DT = 70 ÷ 0.989 = 71 years.
| Growth rate | Doubling time |
|---|---|
| 0.5% | 140 years |
| 1% | 70 years |
| 2% | 35 years |
| 3.5% | 20 years |
Real example: Japan is shrinking (−0.76%), so it has no doubling time at all.
It is only an estimate: The rule of 70 assumes the growth rate stays the same. Births, deaths and migration change, so a doubling time is a forecast, not a fact.
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The crude birth rate counts births for everyone, even men and grandparents. The total fertility rate counts children per woman, so it shows the future better.
Total fertility rate
- Total fertility rate (TFR) = the average number of children a woman would have in her lifetime.
- It counts births per woman of childbearing age, unlike the crude birth rate (per 1000 people).
- Replacement level is about 2.1: two children replace the parents, plus a little for children who die young.
- TFR below 2.1 for many years: in time the population falls and ages, unless immigrants arrive.
- TFR above 2.1: the population keeps growing.
Real example: South Korea's TFR was 0.72 in 2023 and 0.75 in 2024, the lowest in the world. In Niger women have about six children each.
Per woman, not per 1000: TFR is about families, not the whole population: 'children per woman'. Size of the population does not come into it.
Life expectancy sums up how healthy and safe a place is.
Life expectancy
- Life expectancy = the average number of years a person can expect to live, usually from birth.
- It assumes today's death rates stay the same for the rest of their life.
- Higher with good healthcare, a healthy diet and enough income to afford it.
- Higher with clean water and sanitation, and less air pollution.
- Lower after wars, famines and pandemics.
Healthcare
- Japan: everyone is covered by health insurance and sees a doctor often.
Diet and income
- Japan: a diet rich in fish and vegetables, and incomes high enough to afford it.
Clean water and air
- Piped, treated water and sewers stop diseases like cholera.
Real example: Japan's life expectancy is about 84 years (women 87, men 81), against a world average of 73.3 (2024).
Give the reason, not a label: 'Better quality of life' alone is not enough. Say what is better: healthcare, diet, clean water, less pollution.
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Papers ask for the similarities and differences between two measures. Learn what each one counts.
Comparing the measures
- All four measures are averages (mean values), usually for one year.
- CBR: births per 1000 of the whole population; a snapshot of one year.
- TFR: births per woman, over her lifetime; it allows for the age of the women.
- NIR: births and deaths; it can be negative; it shows growth better than CBR alone.
- DT: an estimate from the growth rate; it takes deaths into account, CBR does not.
- Together they let us compare populations and predict change.
| Measure | Counts | Unit | Can be negative? |
|---|---|---|---|
| Crude birth rate | Births in the whole population | Per 1000 per year | No |
| Total fertility rate | Children per woman, lifetime | Children per woman | No |
| Natural increase rate | Births minus deaths | % or per 1000 | Yes |
| Doubling time | Years to double | Years | No (none if shrinking) |
| Life expectancy | Average years lived | Years | No |
Real example: Japan, 2024: CBR 5.7 per 1000, TFR 1.15, NIR −0.76%, no doubling time, life expectancy about 84. Together they show a shrinking, ageing population.
How a [4] is marked: One mark per point: a definition, a similarity, a difference. Give both sides: only similarities or only differences caps the answer at [3].
Papers also hand you a graph, a map or a table of population data. Read it the same way every time.
How to read population data
- Describe the trend: rising, falling or steady, and when it changes.
- Give the rate of change: slow, rapid, exponential, slowing down.
- Quote numbers and years from the graph.
- A fall in the line = negative growth that year.
- Compare places or regions: which is highest, which is lowest.
- Population density = population ÷ area (people per km²).
Start
Iceland: no people before about 874, when settlers arrived.
Slow rise
About 50,000 people by 1703.
A fall
The Laki eruption of 1783 and famine killed about a fifth.
Rapid rise
Fast growth after 1900, to about 390,000 today.
Trend, rate, differences: When describing population data, state the trend (rising or falling), the rate of change, and any differences between places, with numbers.
Real example: describing Iceland's line in four steps, each with a date and a number, would earn the marks on a [2] 'describe the trends' question.
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How this comes up: Calculate a natural increase rate or a doubling time from a fact file or table [1]; a crude death rate [1]; what a fertility rate means for the future [1]; why life expectancy is higher [1]; describe trends [2]; compare two measures, or outline demographic tools [4].
In 2024 Japan had a crude birth rate of 5.7 per 1000 and a natural increase rate of −0.76%.
Outline the similarities and differences between crude birth rate and natural increase rate.
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