Circular Flow of Income and National Income Accounting

The circular flow model shows how money moves around an economy through spending, income, and production. National income accounting puts numbers on that flow. Together, they form the foundation for understanding how economists measure the size and health of an economy.

The Circular Flow of Income¶

Two-Sector Model¶

In the simplest model, the economy has only two groups: households and firms.

• Households own the factors of production (land, labour, capital, enterprise) and supply them to firms.
• Firms use those factors to produce goods and services, paying households rent, wages, interest, and profit in return.
• Households spend their income on the goods and services firms produce.

This creates a continuous loop. Money flows from firms to households as factor payments, and from households back to firms as expenditure on goods and services.

In this two-sector model, with no saving and no spending outside the loop:

$$\text{Income (Y)} = \text{Output (Q)} = \text{Expenditure (AE)}$$

This is why there are three ways to measure national income — they all measure the same circular flow from different angles.

Including Leakages and Injections¶

Once we allow households to save and firms to invest, the simple loop breaks:

• Savings (S) — income earned but not spent — leak out of the consumption flow.
• Investment (I) — firms borrow and spend on new capital — inject money back in.

Equilibrium in the two-sector model requires:

$$S = I$$

If saving exceeds investment, total expenditure is less than output; firms see unsold stock and cut production. If investment exceeds saving, demand exceeds output and production rises until they equalise.

Three-Sector Model (Including Government)¶

Adding government introduces two more flows:

• Taxation (T) — a leakage from household income to government.
• Government spending (G) — an injection of funds back into the economy.

Aggregate expenditure becomes:

$$AE = C + I + G = Y$$

Equilibrium using the injection-leakage approach:

$$I + G = S + T$$

Investment and government spending together must equal saving and taxation together. Even if firms invest less than households save, the economy stays in equilibrium if government spending exceeds taxation by the same gap (a budget deficit).

Four-Sector Model (Including the Foreign Sector)¶

Adding the foreign sector completes the model:

• Imports (M) — money leaves the domestic economy (a leakage).
• Exports (X) — money enters from abroad (an injection).

Aggregate expenditure:

$$AE = C + I + G + (X - M) = Y$$

Equilibrium:

$$S + T + M = I + G + X$$

All leakages (saving, taxation, imports) must equal all injections (investment, government spending, exports).

National Income Accounting¶

National income is the total money value of goods and services produced in an economy over a given period, usually one year.

Key Concepts¶

Gross Domestic Product (GDP) is the total market value of all final goods and services produced within a country's borders during a year, regardless of who owns the factors of production.

Gross National Product (GNP) is the total market value of all final goods and services produced by the nationals (residents) of a country, whether produced domestically or abroad.

$$GNP = GDP + \text{Net Factor Income from Abroad (NFIA)}$$

NFIA is the difference between income earned by the country's nationals abroad and income earned by foreigners within the country.

Net National Product (NNP) is GNP minus depreciation (capital consumption).

$$NNP = GNP - \text{Depreciation}$$

NNP is equivalent to National Income (NI).

The Three Methods of Calculating GDP¶

All three methods should yield the same result — they measure the same flow at different points in the circular flow.

1. The Expenditure Method

Adds up all spending on final goods and services:

$$GDP = C + I + G + (X - M)$$

Where:

• $C$ = household consumption
• $I$ = investment (business spending on new capital, including changes in inventories)
• $G$ = government spending on goods and services (excludes transfer payments like pensions)
• $X - M$ = net exports (exports minus imports)

2. The Income Method

Adds up all factor incomes earned in production:

$$GDP = \text{Wages} + \text{Rent} + \text{Interest} + \text{Profit}$$

Adjustments: add indirect taxes, subtract subsidies to move from factor cost to market prices. Transfer payments (pensions, unemployment benefits) are excluded because they do not represent payment for current production.

3. The Output (Value-Added) Method

Adds up the value added at each stage of production across all industries. Value added = value of output at each stage minus cost of inputs purchased from other firms.

This method avoids double counting — counting the value of intermediate goods (inputs) more than once.

GDP at Market Price vs Factor Cost¶

GDP at market price includes indirect taxes but has not deducted subsidies.

GDP at factor cost reflects what producers actually receive:

$$GDP_{\text{factor cost}} = GDP_{\text{market price}} - \text{Indirect taxes} + \text{Subsidies}$$

Nominal vs Real GDP¶

Nominal GDP measures output at current prices. It rises when either the physical quantity of goods produced rises or when prices rise.

Real GDP adjusts for inflation by measuring output at the prices of a fixed base year. Real GDP rises only when the actual quantity of goods and services increases.

$$\text{Real GDP} = \frac{\text{Nominal GDP}}{\text{Price Index}} \times 100$$

Potential GDP is the maximum output an economy can sustain without causing inflation — the level achievable when all resources are fully and efficiently employed. If actual GDP falls below potential GDP, the economy has a negative output gap and is operating inefficiently.

Nominal vs Real Output Growth¶

Nominal output growth is the percentage change in nominal GDP. Real output growth is the percentage change in real GDP. Only real output growth represents an actual improvement in the economy's productive capacity and living standards.

Uses of National Income Statistics¶

• Measuring economic growth over time
• International comparisons of living standards
• Informing government fiscal and monetary policy decisions
• Identifying sectors of the economy that are growing or contracting
• Tracking changes in income distribution

FLASHCARD SET • 8 CARDSCircular Flow and National Income: Quick Recall