IB Economics HLTopic 4 — The Global EconomyPaper 1, 2 & 3Core skill~11 min read
Single Indicators of Development
A single indicator measures one thing. That is its strength and its weakness. Used well it gives you a sharp, comparable number; used carelessly it lets you describe two completely different countries as if they were the same.
📚 What you need to know
A single indicator measures one characteristic of development.
Real GDP is output adjusted for inflation; GDP per capita divides it by population.
GNI adds income earned abroad by a country’s citizens.
Purchasing power parity (PPP) adjusts for differences in the cost of living.
Other families of indicators cover health, education, inequality, energy and environment.
Every single indicator hides the distribution behind the average.
Income indicators
The two you must be able to calculate
Real GDP = (nominal GDP ÷ price index) × 100
GDP per capita = real GDP ÷ population real strips out inflation, per capita strips out population size
Both adjustments do the same job in different directions. Real GDP stops you mistaking higher prices for higher output. Per capita stops you mistaking a bigger population for a richer one. A country can double its output and still see living standards fall if the population trebles.
Textbooks often shortcut the inflation adjustment by subtracting the inflation rate: 100bn with 10% inflation becomes 90bn. That is close but not right. Dividing by 1.10 gives 90.9bn. Use the division method — it is the one that matches the mark scheme when the numbers get bigger.
GNI and why it differs from GDP
GDP counts output produced inside the borders. GNI counts income earned by the country’s citizens wherever they are, so it includes money sent home from abroad and excludes profits foreign firms take out.
For countries with large numbers of workers overseas, or with heavy foreign ownership of their industries, the two numbers can be far apart. GNI per capita usually tells you more about what people actually have to spend.
Purchasing power parity
Converting incomes at market exchange rates makes low-income countries look poorer than they are, because non-traded things like rent, food and haircuts cost far less there. PPP corrects for that by asking how many units of local currency buy what one dollar buys in the United States.
The rule of thumb. Comparing living standards between countries? Use real GNI per capita at PPP. It is the version that adjusts for inflation, population, foreign income and the cost of living all at once.
What the average hides
This one diagram answers most “evaluate the use of GDP per capita” questions. A mean tells you nothing about the spread.
The other families of indicator
Energy indicators are the ones students always forget. Electricity generation per person is a surprisingly good proxy for whether an economy can industrialise at all.
Indicator
What it captures well
What it misses
Real GDP per capita
Average material output available per person
Distribution, unpaid work, the informal economy, environmental cost
Real GNI per capita at PPP
Income actually available to citizens, cost-of-living adjusted
Still an average, and PPP baskets are estimates
Infant mortality rate
Health, nutrition and sanitation all at once, and it responds quickly
Nothing about adults, incomes or opportunity
Adult literacy rate
The stock of basic human capital in the workforce
Quality of schooling and whether skills match the jobs available
Gini coefficient
How evenly income is spread
Whether the whole distribution is high or low
CO2 emissions per person
The environmental cost of the current growth path
Emissions embedded in imported goods, which are counted elsewhere
Infant mortality is my favourite single indicator to bring into an essay. It moves within a couple of years of a policy change, it is hard to fake, and it reflects clean water, food, hospitals and maternal education simultaneously. If a data question gives it to you, use it.
Worked examples
WORKED EXAMPLE 1
A country’s nominal GDP is $110bn. Prices are 10% higher than in the base year and the population is 12 million. Calculate real GDP and real GDP per capita. [4]
Step 1: strip out inflation
The price index is 110, so real GDP = (110 ÷ 110) × 100 = $100bnStep 2: divide by population$100bn ÷ 12m = $8,333Real GDP $100bn; real GDP per capita $8,333divide by the index, never subtract the inflation rate — subtracting 10% would have given $99bn
WORKED EXAMPLE 2
GNI per capita is 10,000 pesos. The market exchange rate is 5 pesos per dollar. A standard basket costs 250 pesos locally and $100 in the United States. Calculate GNI per capita at market rates and at PPP, and comment. [4]
Step 1: at the market rate10,000 ÷ 5 = $2,000Step 2: find the PPP rate
The basket costs 250 pesos and $100, so 250 ÷ 100 = 2.5 pesos per dollarStep 3: at PPP10,000 ÷ 2.5 = $4,000Step 4: comment
The market rate understates living standards by half, because non-traded goods and services are much cheaper locally.
$2,000 at market rates, $4,000 at PPP — use the PPP figure for comparison
💡 Exam tip
Show the division for real GDP. The mark is usually for the method, not the answer.
Name the full version — real GNI per capita at PPP — when asked for the best income measure.
Every evaluation of a single indicator should mention distribution. It is the strongest single criticism.
Pick indicators from different families when a question asks you to compare two countries.
Say what an indicator is good for, not just what it misses. Balanced beats cynical.
⚠ Common mix-up
Nominal is not real. If the question mentions prices or inflation at all, adjust.
GDP is not GNI. GDP is where output happens; GNI is who earns the income.
PPP is not an exchange rate forecast. It is a conversion tool for comparing living costs.
A higher Gini is worse, not better. Closer to 1 means more unequal.
Growth is not development. A single income indicator measures the first, not the second.
Up next: Composite Indicators of Development — what happens when you combine several of these into one number, and what that fixes.
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