Syllabus points
- Explain the circular flow of income model.
- Define and distinguish GDP, GNI, nominal and real values, and per-capita measures.
- Explain the use of purchasing power parity (PPP) for comparisons.
- Evaluate GDP and GNI as measures of living standards.
The circular flow of income
The circular flow shows income moving between households and firms. Households supply factors of production and receive income (wages, rent, interest, profit); they spend it on firms' output. In an open economy with a government, the flow includes injections — investment (I), government spending (G) and exports (X) — and leakages (withdrawals) — saving (S), taxation (T) and imports (M).
National income is in equilibrium when injections = leakages: I + G + X = S + T + M.
Key definitions
| Term | Exam-ready definition |
|---|---|
| GDP | The total value of all goods and services produced within a country in a year. |
| GNI | GDP plus net income (property income) from abroad. |
| Real value | A value adjusted for inflation, in constant prices. |
| Purchasing power parity (PPP) | An exchange rate that equalises the price of a basket of goods across countries. |
Measures of national income
- Nominal GDP is measured in current prices; real GDP is adjusted for inflation and shows genuine changes in output.
- GDP per capita divides GDP by population, giving a better guide to average living standards.
- GNI adds net income from abroad — important for countries with large flows of profit or remittances.
- PPP exchange rates allow fairer comparisons than market exchange rates, because they account for differences in the cost of living.
Evaluating GDP/GNI as living-standards measures
National income figures are useful but incomplete. They omit the distribution of income (averages hide inequality), unpaid and informal-economy activity, the value of leisure, and negative externalities such as pollution and resource depletion. Composite measures such as the Human Development Index are therefore used alongside GDP.
Worked example
An economy's nominal GDP rises 6% while inflation is 4%. Real GDP growth is approximately 6% − 4% = 2%. Only the real figure reflects a genuine increase in output; if population also grew by 2%, real GDP *per capita* would be roughly unchanged, so average living standards may not have improved.
Common exam mistakes
- Confusing nominal (current prices) with real (inflation-adjusted) GDP.
- Treating GDP as a complete measure of welfare.
- Confusing GDP (output within a country) with GNI (which adds net income from abroad).
Exam technique
Calculate real and per-capita figures from data, then *evaluate* the limitations of GDP/GNI as measures of living standards — a frequent Paper 1 and Paper 2 requirement.
Quick revision
- Injections (I, G, X) vs leakages (S, T, M); equilibrium when equal.
- Real GDP ≈ nominal − inflation; GDP per capita adjusts for population.
- GNI = GDP + net income from abroad; PPP aids comparison.
- GDP ignores inequality, informal activity and the environment.