Economics · Lesson 18

National income: concepts & measurement

JAMBWAECNECO

What the syllabus asks

JAMB: National income: concepts (GNP, GDP, NI, NNP); measurement and problems; uses and limitations of national income estimates; circular flow of income (two-sector model); elementary theory of income determination: consumption, saving, investment, the multiplier

WAEC: National income: meaning and concepts (GDP, GNP, NNP, national income, personal and disposable income, per capita income); circular flow of income; methods of measurement (output, income, expenditure); problems of measurement; uses and limitations of national income statistics; nominal and real income; consumption, saving and investment; the multiplier (simple treatment)

NECO: National income: meaning and concepts (GDP, GNP, NNP, national income, personal and disposable income, per capita income); circular flow of income; methods of measurement (output, income, expenditure); problems of measurement; uses and limitations of national income statistics; nominal and real income; consumption, saving and investment; the multiplier (simple treatment)

What you will learn

Explain the circular flow of income, injections and leakages.
Define and calculate GDP, GNP, NNP, national income, personal and disposable income.
Measure national income by the output, income and expenditure methods.
Distinguish nominal from real income and calculate per capita income.
Explain the uses, problems and limitations of national income statistics in Nigeria.
Explain consumption, saving and the multiplier.

Key points

National income: total value of final goods and services produced by residents in a year.
Circular flow: output = income = expenditure; injections I, G, X; leakages S, T, M.
GNP = GDP + NFIA; NNP = GNP − depreciation; NI = NNP at factor cost (− indirect taxes + subsidies).
Personal income = NI − retained profits − company tax + transfers; disposable = personal − income tax.
Output method uses value added to avoid double counting.
Income method adds wages, rent, interest and profit; transfer payments excluded.
Expenditure method: C + I + G + (X − M).
Real income removes inflation; NBS rebased GDP in 2014 (base 2010) and 2025 (base 2019).
Problems in Nigeria: subsistence and informal sectors, poor records, unreliable data.
Multiplier = 1 ÷ (1 − MPC) = 1 ÷ MPS.

Start here: Meaning of national income; the circular flow

Every year, Nigerian farmers grow crops, factories make cement and drinks, banks and hospitals provide services. The total value of all this production is the country’s national income. It tells us how big the economy is and whether it is growing.

National income is the total money value of all final goods and services produced by the residents of a country in a given period, usually one year. Because production generates incomes and is bought with spending, it can be measured as output, income or expenditure.

The two-sector circular flow

In a simple economy with only households and firms:

Households supply factor services (labour, land, capital, enterprise) to firms.
Firms pay factor incomes (wages, rent, interest, profit) to households.
Households spend their incomes on goods and services produced by firms.
So total output = total income = total expenditure.

Injections and leakages (withdrawals)

Leakages (out of the flow)	Injections (into the flow)
Savings (S)	Investment (I)
Taxes (T)	Government spending (G)
Imports (M)	Exports (X)

National income is in equilibrium when total injections = total leakages: I + G + X = S + T + M. If injections exceed leakages, income rises; if leakages exceed injections, income falls.

Worked example 18.1

In an economy (illustrative, ₦ billion), I = 400, G = 600, X = 500, S = 450, T = 550, M = 600. Is national income rising, falling or in equilibrium?

Injections = 400 + 600 + 500 = 1,500.
Leakages = 450 + 550 + 600 = 1,600.
Leakages exceed injections by 100: income will fall.

Falling (leakages exceed injections by ₦100bn)

⚠️ Common mistake: listing exports as a leakage. Exports bring money into the country: an injection. Imports are the leakage.

Try it yourself. Is a tax on salaries an injection or a leakage?

Show solution

A leakage: it takes income out of the spending flow.

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Practice questions

1. National income is the total value of

final goods and services produced in a country in a year
all goods including intermediate goods
money in circulation
government spending

Show answer

A: final goods and services produced in a country in a year
Final output only, to avoid double counting.

2. GDP plus net factor income from abroad gives

NNP
national income
disposable income
GNP

Show answer

D: GNP
GNP = GDP + NFIA.

3. NNP equals GNP minus

subsidies
transfer payments
depreciation (capital consumption)
indirect taxes

Show answer

C: depreciation (capital consumption)
Net = after allowing for worn-out capital.

4. GDP = ₦5,000bn and NFIA = −₦200bn. GNP is

₦200bn
₦4,800bn
₦5,200bn
₦5,000bn

Show answer

B: ₦4,800bn
5,000 − 200.

5. The output (value added) method avoids

double counting
inflation
depreciation
transfer payments

Show answer

A: double counting
Count only value added at each stage.

Key words

National income: Total money value of all final goods and services produced by a country’s residents in a year, after depreciation, at factor cost.
Gross domestic product (GDP): Total value of final goods and services produced within a country’s borders in a year.
Gross national product (GNP): GDP plus net factor income from abroad.
Net factor income from abroad: Factor incomes earned abroad by residents minus factor incomes earned at home by foreigners.
Depreciation: Value of capital worn out in producing output; also called capital consumption allowance.
Net national product (NNP): GNP minus depreciation.
Factor cost: Value of output measured by payments to factors, excluding indirect taxes and including subsidies.
Market prices: Prices paid by buyers, including indirect taxes and net of subsidies.
Value added: Value of a firm’s output minus the value of intermediate inputs bought from other firms.
Double counting: Counting the value of an intermediate good more than once.
Transfer payment: Payment not made in return for current productive service, e.g. pensions, gifts.
Personal income: Income actually received by households before personal income tax.

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