Demographic data describes a population: its size, its rates of birth and death, and its age structure. In IGCSE Economics you meet it in data tables and short extracts, and you are expected to read the unit and the date of every figure before calculating anything. This lesson belongs to the development, population and environment module.
What do the units actually mean?
A figure without a unit can mean three different things. Always ask three questions: what is being counted, over what period, and relative to what base.
- Population is a count at a date, such as 8.4 million in 2025.
- Birth rate and death rate are per 1,000 people, for one year.
- Natural increase is birth rate minus death rate, per 1,000. Divide by 10 for a percentage.
- Dependency ratio is the number of people under 15 and over 64 compared with the number aged 15 to 64, often shown per 100 working-age people.
How do you calculate a change step by step?
- Write down the starting and final figures with their dates.
- Find the change: final minus starting.
- Divide the change by the starting figure and multiply by 100.
- Write the answer with its period, for example “5% over five years”.
Worked example
Narvala is a fictional country. Its population was 8.0 million in 2020 and 8.4 million in 2025.
In 2025 the birth rate was 18 per 1,000 and the death rate was 8 per 1,000. The population aged under 15 was 2.0 million, aged 65 and over was 0.8 million, and aged 15 to 64 was 5.6 million.
Total change: 8.4 − 8.0 = 0.4 million.
Percentage change: 0.4 ÷ 8.0 × 100 = 5% over five years.
Natural increase in 2025: 18 − 8 = 10 per 1,000, which is 1.0% in that year.
Dependency ratio: (2.0 + 0.8) ÷ 5.6 = 0.5, so 50 dependants per 100 working-age people.
Check that the age groups add to the total: 2.0 + 0.8 + 5.6 = 8.4 million. They do, so the data is consistent.
The mistake to watch for
A student reads the table and writes: “Narvala’s population grows by 5% a year.”
Mistaken answer: the population grew by 5% each year, so it doubles quickly.
The 5% is the change across five years. Spread evenly, it is a little under 1% a year, close to the 1.0% natural increase in the later year.
The correction is to tie every percentage to its period. Write “5% over five years” and do not call it annual unless the question says so.
Check yourself
1. Brenia’s population was 2.50 million in 2015 and 2.75 million in 2025. Find the percentage change and state the period.
Show answer
Change = 2.75 − 2.50 = 0.25 million. Percentage change = 0.25 ÷ 2.50 × 100 = 10% over ten years.
2. Kolmar has a birth rate of 24 per 1,000 and a death rate of 9 per 1,000. Find the natural increase as a percentage for that year.
Show answer
24 − 9 = 15 per 1,000. Dividing by 10 gives 1.5% in that year.
3. A country has 3.0 million people aged under 15, 1.2 million aged 65 and over, and 7.8 million aged 15 to 64. Find the dependency ratio per 100 working-age people.
Show answer
(3.0 + 1.2) ÷ 7.8 = 4.2 ÷ 7.8 ≈ 0.538. That is about 54 dependants per 100 working-age people.
Where this leads next
Once reading units feels automatic, move on to explaining a human-capital mechanism, then test yourself with the mixed practice set. The percentage-base explorer lets you rehearse the percentage steps with fictional numbers.
Some students can follow every step here but still drop the unit when a longer table appears. That is a habit our teachers look for in online one-to-one Economics tuition.