National Income
Edexcel International A-Level EconomicsΒ· 2.3.4Β· 25 min read
1. 1. Circular Flow of Income & Key Definitionsβ β ββββ± 8 min
Circular Flow of Income
A model showing the flow of goods, services and money between economic agents in an economy, including injections of extra spending and withdrawals of spending from the flow.
Example:
A 2-sector closed economy flow only includes households and firms, while a 3-sector open model adds government and international trade.
First, distinguish between two core macroeconomic terms: income is a flow variable (measured over time, e.g. monthly wages), while wealth is a stock variable (measured at a single point, e.g. value of owned property). The full open-economy circular flow includes three injections (spending added to the flow) and three withdrawals (spending removed from the flow):
Injections (J): Investment (I) by firms, government spending (G), export revenue (X) from overseas buyers
Withdrawals (W): Savings (S) by households, taxation (T) paid to government, import spending (M) on foreign goods
State whether each of the following counts as an injection or withdrawal: a) UK government spending on new hospitals, b) A UK consumer buying a German-made car, c) A UK tech firm investing in new servers.
- 1
a) Government spending is an injection (G)
- 2
b) Spending on imports is a withdrawal (M)
- 3
c) Firm investment is an injection (I)
Exam tip:
For 4-mark diagram questions, label all 3 injections and 3 withdrawals clearly, plus arrows showing flow direction between households, firms, government and the foreign sector.
2. 2. Equilibrium Level of Real National Outputβ β β βββ± 7 min
Equilibrium National Output
The level of real GDP where aggregate demand (AD) equals aggregate supply (AS), with no pressure for prices or output to change in the short run, assuming ceteris paribus.
Equilibrium is plotted on an AD-AS diagram with the price level on the y-axis and real national output on the x-axis. Shifts in AD or AS will move the economy to a new equilibrium level of output and prices. For example, an increase in government spending (an injection) shifts AD right, raising equilibrium real output and the price level, assuming AS is not perfectly inelastic.
Using an AD-AS diagram, explain the effect of a rise in household savings (a withdrawal) on equilibrium national output.
- 1
Draw a standard AD-AS diagram with upward-sloping short-run AS, label initial equilibrium E1 where AD1 intersects SRAS, with output Y1 and price level PL1.
- 2
A rise in savings reduces household consumption, shifting AD left to AD2.
- 3
New equilibrium is E2, with lower real output Y2 and lower price level PL2.
Exam tip:
Always use your diagram in written analysis for 6+ mark questions: reference labels (e.g. 'AD shifts right from AD1 to AD2, raising output from Y1 to Y2') to pick up full KAA marks.
3. 3. The Multiplier Effect & Calculationsβ β β β ββ± 10 min
Multiplier (k)
A measure of how much national income changes following an initial change in injections or withdrawals. The multiplier effect occurs when an initial injection ripples through the economy, generating further rounds of spending.
The multiplier depends on marginal propensities, which measure the proportion of an extra Β£1 of income that is used for a given purpose:
β’ MPC: Marginal propensity to consume = proportion of extra income spent on domestic goods
β’ MPS: Marginal propensity to save = proportion of extra income saved
β’ MPT: Marginal propensity to tax = proportion of extra income paid in tax
β’ MPM: Marginal propensity to import = proportion of extra income spent on imports
The marginal propensity to withdraw (MPW) = MPS + MPT + MPM, so the two standard multiplier formulas are:
Calculate the value of the multiplier if MPC = 0.6, and find the total change in national income following an initial Β£20bn increase in government investment.
- 1
- 2
Total change in national income = initial injection Γ multiplier = Β£20bn Γ 2.5 = Β£50bn.
- 3
This means the Β£20bn initial injection generates a total Β£50bn rise in national income, as the extra spending ripples through the economy.
Exam tip:
For calculation questions, always show your full working: even if your final answer is wrong, you can pick up 1 mark for correctly writing the multiplier formula.
4. Common Pitfalls
Wrong move:
Confusing income and wealth, defining both as stock variables.
Why:
Income is a flow measured over time, wealth is a stock measured at a point in time, mixing them loses definition marks.
Correct move:
Explicitly state income = flow, wealth = stock in all definition answers.
Wrong move:
Forgetting exports are an injection and imports are a withdrawal, reversing them.
Why:
Exports bring spending into the domestic economy, imports take spending out, so misclassification leads to wrong circular flow analysis.
Correct move:
Memorise J = I, G, X; W = S, T, M, and check if spending flows into or out of the domestic economy.
Wrong move:
Calculating the multiplier as 1/MPC instead of 1/(1-MPC).
Why:
This common arithmetic error leads to incorrect multiplier values, losing full calculation marks.
Correct move:
Write the formula explicitly before substituting values to avoid mistakes.
Wrong move:
Drawing the multiplier effect as a shift in AS instead of a larger shift in AD.
Why:
The multiplier only affects the size of AD shifts, so incorrect diagram labelling loses 2+ marks.
Correct move:
Label initial AD1, shift from initial injection to AD2, final AD3 after multiplier effect, with arrows showing the difference between initial and total shift.
Wrong move:
Failing to link the multiplier magnitude to MPW in analysis questions.
Why:
Higher MPW means a smaller multiplier, as more extra income leaks out of the circular flow in each round of spending.
Correct move:
Explicitly state 'the size of the multiplier depends on MPW: higher leakages reduce the multiplier effect' in 6+ mark analysis answers.
5. Quick Reference Cheatsheet
Concept | Key Formula/Rule | Exam Reminder |
|---|---|---|
Circular Flow | J = I, G, X; W = S, T, M; Equilibrium if J=W | Label all 6 flows clearly on diagram questions |
Equilibrium Output | AD = AS on y(Price Level)/x(Real Output) axes | Reference diagram labels in written analysis |
Multiplier | k = 1/(1-MPC) = 1/(MPS+MPT+MPM) | Show full working for calculation questions; label AD shifts for multiplier diagrams |
Multiplier Effect | ΞY = Initial Injection Γ k | Higher MPW = lower k, smaller AD shift |
6. Frequently Asked
What is the difference between income and wealth?
Income is a flow variable measured over a period of time (e.g. annual salary), while wealth is a stock variable measured at a single point in time (e.g. value of owned property or savings accounts).
How do I know if the circular flow is expanding?
If total injections (J) are greater than total withdrawals (W), national income rises and the circular flow expands. If W > J, national income falls and the flow contracts.
Going deeper
What's Next
Now that you have mastered national income concepts, you are ready to move to the next core Unit 2 topic: economic growth, output gaps, and the causes and costs of short-run and long-run growth. You will use your understanding of AD-AS equilibrium and the multiplier to analyse how policy changes affect long-run economic performance, and evaluate the trade-offs between growth, inflation and unemployment. You can also practice exam-style questions on national income to test your understanding of diagram drawing, multiplier calculations and chain analysis for 6+ mark answers. Make sure you memorise the multiplier formulas and circular flow definitions ahead of your Unit 2 exam, as these are frequently tested in both short answer and extended response questions.