Pay a decorator to paint your house and national income rises. Paint it yourself and it does not. Marry your cleaner and, as the old joke has it, GDP falls. The work is identical in all three cases and only the transaction changes. Every figure quoted in macroeconomics rests on a measure built from transactions, and knowing precisely what it counts, and what it silently ignores, is the difference between using the statistics and being misled by them.
Gross domestic product
The total value of all final goods and services produced within a country's borders in a given period.
Two words in that definition do real work. Final excludes intermediate goods, because counting the steel and then counting the car containing it would double count the same value. Within a country's borders makes GDP a measure of location rather than ownership, so output produced by a foreign-owned factory counts towards the host country's GDP and not the owner's.
The same total can be reached by three routes, and in principle they give the same answer. The output method sums the value added at each stage of production. The income method sums the incomes earned by the factors of production: wages, rent, interest and profit. The expenditure method sums what is spent on final output, which is consumption plus investment plus government spending plus net exports. They are equal because every pound of output generates exactly a pound of income for someone and is bought by someone for exactly a pound. In practice the three estimates differ, and statistical agencies reconcile them with a balancing item, which is itself a reminder that these figures are estimates rather than measurements.
GNI = GDP + net primary income from abroad and Real GDP = (nominal GDP / GDP deflator) x 100Net primary income from abroad is income earned by domestic residents overseas minus income earned by foreigners domestically. It is the difference between where output is produced and who receives the income from it. Formulae are not printed in any 9708 paper, so recall both.
Two further adjustments turn one measure of national income into another, and each removes something that is not really output. The first is from market prices to basic prices. Market prices include indirect taxes such as VAT and are reduced by subsidies, so they overstate or understate what producers actually receive. Deducting taxes on products and adding back subsidies gives national income at basic prices, the value received by the factors of production. The second is from gross to net. Every year part of the capital stock wears out or becomes obsolete, and some investment merely replaces it. That loss is called depreciation or capital consumption. Deducting it from gross domestic product gives net domestic product, and deducting it from gross national income gives net national income (NNI), which is the value of output an economy could consume without running down its capital.
GDP at basic prices = GDP at market prices - taxes on products + subsidies on products. NNI = GNI - depreciationGross means before depreciation, net means after it. Market prices means including indirect taxes and subsidies, basic prices means excluding them. Questions often give all the figures and ask for one particular measure, so name the measure you are calculating before you start.
The GDP against GNI distinction is worth marks whenever a question involves foreign investment or a developing economy. A country hosting large multinational operations can have GDP well above GNI, because profits are produced inside its borders but repatriated to owners abroad. Saying that GDP overstates the income actually available to residents in such a case is a precise point that examiners credit and most candidates miss.
Stripping inflation out with the GDP deflator
A country's nominal GDP is $600 billion. The GDP deflator stands at 125, with the base year set at 100. Calculate real GDP at base year prices. Then explain what it would mean if nominal GDP rose to $660 billion the following year while the deflator rose to 137.5.
The circular flow
The circular flow of income is the model that makes the three measurement methods intelligible. In the simplest version, households supply factors of production to firms and receive income in return, then spend that income on the output firms produce. Income flows one way and goods the other, and the two flows are equal because they are the same transactions viewed from opposite ends. This is why national output, national income and national expenditure are three names for one quantity.
A real economy is not closed, so the flow leaks and is topped up. Withdrawals are income that leaves the domestic circular flow: saving, taxation and spending on imports. Injections are spending that enters it from outside the household-firm loop: investment, government spending and exports. National income is in equilibrium when total injections equal total withdrawals. When injections exceed withdrawals, income rises; when withdrawals exceed injections, income falls. Notice that equilibrium here means unchanging, not desirable, and an economy can sit in equilibrium with high unemployment indefinitely.
Draw a circular flow diagram with households and firms. Show the income flow and the expenditure flow between them. Then add the three withdrawals (saving, taxation, imports) leaving the flow and the three injections (investment, government spending, exports) entering it, labelling each with the sector it passes through: the financial sector, the government and the foreign sector.
Pair each withdrawal with the injection that returns through the same sector: saving with investment through the financial sector, taxation with government spending, imports with exports. Equilibrium requires the totals to match, not each pair individually, and questions often turn on that distinction. A country can run a trade deficit indefinitely provided the shortfall is offset elsewhere in the flow.
How an injection raises national income by more than itself
- Firms increase investment spending, which is an injection into the circular flow.
- The firms supplying the machinery receive that spending as revenue, and it becomes income for their workers and owners.
- Those households spend a proportion of the extra income on domestic goods and services.
- That spending becomes income for a further set of households, who spend a proportion of it in turn.
- Each round is smaller than the last, because a share of income leaks out as saving, taxation and imports at every stage.
- The rounds form a converging series, so the total increase in national income is finite but larger than the original injection.
- The economy settles at a new equilibrium where withdrawals have risen enough to match the higher injections.
The last step is the one worth understanding rather than memorising. The multiplier process stops precisely when the extra withdrawals generated by the higher income equal the original injection, which is why the size of the multiplier is determined by the marginal propensity to withdraw. The arithmetic is worked through in the fiscal policy note.
Practise this chain →In a four-sector circular flow, national income is in equilibrium when:
A country hosts extensive foreign-owned manufacturing. Which is most likely?
Applied context
Ireland provides the clearest illustration of the GDP and GNI gap in an advanced economy. A concentration of multinational activity, including the relocation of intellectual property assets, produced GDP figures substantially above any plausible measure of domestic economic activity, most dramatically in 2015 when measured GDP growth was reported at over 20% without any corresponding change in living standards. The Irish statistical office subsequently developed a modified national income measure specifically to strip out these distortions. The episode is useful because it shows a wealthy, well-administered economy encountering the same conceptual problem usually discussed in a developing-country context.
This example is strong precisely because it is not about measurement error or weak statistical capacity. The figures were correct; the concept was simply not measuring what readers assumed it measured.