# National Income

> Edexcel International A-Level Economics · IAL Economics 2018
> Source: https://www.owlsprep.com/study/edexcel-ial-economics-u2-national-income/

This guide covers core national income concepts for Edexcel IAL Economics Unit 2: circular flow of income, equilibrium national output, and the multiplier effect, including exam-standard calculations and diagrams.

**Prerequisites:** [Aggregate Demand (AD) components](https://www.owlsprep.com/study/edexcel-ial-economics-u2-aggregate-demand/); [Aggregate Supply (AS) curves](https://www.owlsprep.com/study/edexcel-ial-economics-u2-aggregate-supply/)

## Learning objectives

- Distinguish between income and wealth, and identify injections/withdrawals in the circular flow of income
- Explain how equilibrium national output is determined using AD-AS, and how curve shifts change this equilibrium
- Calculate the multiplier using MPC and MPW, and explain its effect on the magnitude of AD shifts
- Draw exam-standard diagrams for circular flow and the multiplier effect for written questions

## 1. Circular Flow of Income & Key Definitions

**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

> **info**
>
> If J > W, national income rises; if J < W, national income falls; if J = W, the circular flow is in equilibrium, with no short-run change to national income.

**Worked example:** 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. Equilibrium Level of Real National Output

**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.

**Worked example:** 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. The Multiplier Effect & Calculations

**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 £1 of income that is used for a given purpose: <br>• MPC: Marginal propensity to consume = proportion of extra income spent on domestic goods <br>• MPS: Marginal propensity to save = proportion of extra income saved <br>• MPT: Marginal propensity to tax = proportion of extra income paid in tax <br>• MPM: Marginal propensity to import = proportion of extra income spent on imports <br>The marginal propensity to withdraw (MPW) = MPS + MPT + MPM, so the two standard multiplier formulas are:

$$k = \frac{1}{1 - MPC}$$

$$k = \frac{1}{MPW}$$

**Worked example:** Calculate the value of the multiplier if MPC = 0.6, and find the total change in national income following an initial £20bn increase in government investment.

1. $$k = \frac{1}{1 - MPC} = \frac{1}{1 - 0.6} = \frac{1}{0.4} = 2.5$$
2. Total change in national income = initial injection × multiplier = £20bn × 2.5 = £50bn.
3. This means the £20bn initial injection generates a total £50bn rise in national income, as the extra spending ripples through the economy.

> **warning**
>
> The multiplier only applies to changes in injections or withdrawals: shifts in AS do not trigger the multiplier effect. For diagrams, label the initial AD shift (due to the injection) and the larger final AD shift to show the multiplier effect clearly.

> **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.

## Common pitfalls

- **Wrong:** Confusing income and wealth, defining both as stock variables.
  - Why it fails: Income is a flow measured over time, wealth is a stock measured at a point in time, mixing them loses definition marks.
  - Correct: Explicitly state income = flow, wealth = stock in all definition answers.
- **Wrong:** Forgetting exports are an injection and imports are a withdrawal, reversing them.
  - Why it fails: Exports bring spending into the domestic economy, imports take spending out, so misclassification leads to wrong circular flow analysis.
  - Correct: Memorise J = I, G, X; W = S, T, M, and check if spending flows into or out of the domestic economy.
- **Wrong:** Calculating the multiplier as 1/MPC instead of 1/(1-MPC).
  - Why it fails: This common arithmetic error leads to incorrect multiplier values, losing full calculation marks.
  - Correct: Write the formula explicitly before substituting values to avoid mistakes.
- **Wrong:** Drawing the multiplier effect as a shift in AS instead of a larger shift in AD.
  - Why it fails: The multiplier only affects the size of AD shifts, so incorrect diagram labelling loses 2+ marks.
  - Correct: 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:** Failing to link the multiplier magnitude to MPW in analysis questions.
  - Why it fails: Higher MPW means a smaller multiplier, as more extra income leaks out of the circular flow in each round of spending.
  - Correct: Explicitly state 'the size of the multiplier depends on MPW: higher leakages reduce the multiplier effect' in 6+ mark analysis answers.

## 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 | ΔY = Initial Injection × k | Higher MPW = lower k, smaller AD shift |

## 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.

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