IB Economics SLTopic 4 — The Global EconomyPaper 2Core skill~9 min read
Single Indicators of Development
A single indicator measures one thing. GDP per person, life expectancy, literacy, emissions per head. Each is useful and each is partial, and the skill being tested is knowing exactly what your chosen number can and cannot tell you about a country.
📘 What you need to know
A single indicator measures one characteristic of development, such as GDP per capita or infant mortality.
Real GDP is the value of output in a year adjusted for inflation. Nominal GDP is not.
GDP per capita is GDP divided by population, which allows comparison between countries of different sizes.
GNI adds the income citizens earn abroad, so it can differ a lot from GDP where remittances or foreign-owned firms are large.
Purchasing power parity (PPP) adjusts for the fact that the same money buys more in some countries than others.
GNI per capita at PPP is therefore the most comparable single income measure.
Other categories: health (life expectancy, infant mortality, doctors per 1,000), education (literacy, mean years of schooling), inequality (the Gini coefficient), energy and environment (emissions per person, forest area).
Every single indicator is an average, and averages hide how the total is distributed.
Getting the income measure right
Three adjustments turn a raw GDP figure into something worth comparing. Take them one at a time, because Paper 2 will ask you to do exactly this.
From raw output to a comparable income figure
adjust for inflation → divide by population → adjust for what money buys locally
WORKED EXAMPLE
Nominal GDP is $440bn and the GDP deflator is 110. Population is 25 million. Calculate real GDP and real GDP per capita. [4]
Step 1: the formulareal GDP = nominal GDP ÷ (price index ÷ 100)Step 2: substitute440 ÷ 1.10 = $400bnStep 3: divide by population400,000,000,000 ÷ 25,000,000 = $16,000Real GDP $400bn; real GDP per capita $16,000Do not take 10% off the nominal figure. That gives $396bn, which is wrong, because prices rose by 10% rather than the total being 10% too big.
That last note catches out a lot of students, and some textbooks too. Dividing by 1.10 and subtracting 10% are not the same operation, and the gap grows as inflation rises. Always divide.
WORKED EXAMPLE
A basket of goods costs $60 in the USA and 900 units of local currency at home. The market exchange rate is 20 units per dollar. Average income is 90,000 units. Compare income at market rates and at PPP. [4]
Step 1: find the PPP rate
The rate that makes the basket cost the same in both places.
900 ÷ 60 = 15 units per dollarStep 2: income at the market rate90,000 ÷ 20 = $4,500Step 3: income at PPP90,000 ÷ 15 = $6,000$4,500 at market rates, $6,000 at PPPBecause goods are cheaper locally, the market rate understates what people can actually buy. This is why income comparisons between countries are almost always quoted at PPP.
Why one number is never enough
Here are two countries with identical income per person. Every other indicator says they are nothing alike, and a report using only the first row would call them equally developed.
Country B’s average income is being earned by a much narrower group. That is what the higher Gini coefficient is telling you, and it is why average income alone is a weak development measure.
Measuring inequality: the Lorenz curve and the Gini
The Gini coefficient comes from a diagram. Plot the share of income earned by the poorest x per cent of the population. Perfect equality would be a straight diagonal, since the poorest 40% would earn 40% of the income. The real curve sags below it, and how far it sags is the inequality.
A Gini of 0.29 and one of 0.52 describe very different societies with the same average income, which is exactly the gap that income per head cannot see.
The categories of single indicator
Category
Typical indicators
What it captures
Income
GDP or GNI per capita at PPP
Average material living standards
Health
Life expectancy, infant mortality, doctors per 1,000
Whether people live long, healthy lives
Education
Adult and youth literacy, mean years in school
Skills, opportunity and future productivity
Inequality
Gini coefficient, share of women in parliament
How the gains are shared out
Energy
Electricity generation or oil use per person
Industrial capacity and access to power
Environment
Emissions per person, forest area, water use
Whether the growth can be sustained
Choosing an indicator is an argument. If a question hands you a table and asks which country is more developed, say which indicator you are relying on and why, then name one that points the other way. That is application and evaluation in two sentences.
💡 Exam tip
Divide by the price index over 100 to get real values. Never subtract the inflation rate.
Say “per capita at PPP” whenever you compare incomes between countries. It is the accurate phrase and it is quick.
Know one indicator from each category. Questions often ask for two contrasting measures.
Attack the average. Every single indicator is a mean, and means hide distribution.
Use the Gini alongside income. The pairing shows you understand what income per head misses.
Watch the direction of the scale. A high life expectancy is good; a high infant mortality rate is not.
⚠️ Common mix-up
Confusing GDP and GNI. GNI includes income earned abroad by a country’s citizens.
Comparing nominal figures across years, or market-rate figures across countries.
Reading a rise in average income as a rise in everyone’s income. It may only be the top of the distribution.
Thinking a higher Gini is better. Higher means more unequal.
Using one indicator and calling it development. Development is multi-dimensional by definition.
Forgetting data quality. The countries where measurement matters most often have the weakest statistics.
Up next: Composite Indicators: HDI and Beyond — what happens when you combine several of these single measures into one number, and what that number still cannot see.
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