The first four chapters examined how individuals and firms make decisions in specific markets. We now shift scale. Macroeconomics studies the economy as a whole: the total output of goods and services, the overall price level, the unemployment rate, and the patterns of expansion and contraction that define the business cycle.
Before we can analyze these phenomena, we must measure them. This chapter introduces the national accounting framework that quantifies aggregate economic activity. The numbers themselves are not the point. The point is what they reveal about how economies function and what they obscure.
Four words in this definition carry heavy weight:
The circular flow of the economy guarantees that GDP can be measured three equivalent ways:
The three-approaches framework wasn't handed down ready-made — it was invented. Simon Kuznets built the first U.S. national accounts in the 1930s and Richard Stone systematized them into the postwar System of National Accounts. That this is intellectual history, not arithmetic, is taken up in the history-of-economic-thought book's treatment of the postwar synthesis.
1. Expenditure approach: Add up all spending on final goods and services.
| Component | What it includes | Typical share |
|---|---|---|
| $C$ — Consumption | Household spending on goods and services | ~60–70% |
| $I$ — Investment | Business fixed investment, residential investment, inventory changes | ~15–20% |
| $G$ — Government spending | Government purchases of goods and services (not transfer payments) | ~15–20% |
| $NX$ — Net exports | Exports minus imports | Variable (can be negative) |
2. Income approach: Add up all income earned in production.
Every dollar spent on a final good becomes someone's income: wages to workers, rent to landlords, interest to lenders, profit to owners.
3. Production (value-added) approach: Sum the value added at each stage of production.
If a farmer grows wheat (\$1), a miller grinds flour (\$1), and a baker sells bread (\$1), the value added is: \$1 + (\$1 − \$1) + (\$1 − \$1) = \$1 + \$1 + \$1 = \$1 = price of the final good.
All three approaches yield the same GDP. This is an accounting identity, not a theory.
Hover over the arrows to see a description of each flow. The four sectors (Households, Firms, Government, and the Foreign sector) are connected by flows of spending, income, taxes, and transfers.
Figure 7.1. Circular flow diagram. Every dollar of expenditure (C, I, G, NX) becomes income (wages, rent, interest, profits). Government collects taxes and makes transfers. The foreign sector adds exports and subtracts imports.
This diagram has an ancestor. The 18th-century physiocrat François Quesnay drew the first circular-flow picture of an economy in his Tableau économique, building on the political arithmetic of Petty and King — the lineage the history-of-economic-thought book traces under mercantilism, physiocracy, and Hume.
Several boundary cases clarify the GDP concept:
Nominal GDP can rise because the economy produces more stuff or because prices go up. To measure actual production growth, we need to separate the two.
What this says: Real GDP holds prices fixed to a single base year, so the only thing that can change the number is the quantity of stuff actually produced. It strips out price changes and shows you the volume of real output.
Why it matters: When you hear that an economy "grew 3%," that's real GDP. It answers the question that matters for living standards: are we producing more goods and services, or just paying more for the same ones?
See Full Mode for the derivation.Once you can compare real output, the natural next move is to compare it across countries.
For the centuries before modern statistical agencies, real-output estimates have to be reconstructed — the pre-1820 economic cores explorer shows how far back the comparison can be pushed, and how much harder the measurement gets.
What this says: The GDP deflator tells you how much of nominal GDP growth is just price increases rather than real production. If nominal GDP doubled but real GDP stayed the same, the deflator doubled. All that "growth" was inflation.
Why it matters: It lets you strip away inflation to see whether an economy is actually producing more goods and services, or just charging more for the same output.
See Full Mode for the derivation.What this says: The CPI tracks the cost of buying the same fixed basket of everyday goods over time. Fill a cart with what a typical household buys, then check the till each year: if the cart costs 5% more, the CPI rose 5%.
Why it matters: The CPI is the inflation number that shows up in the news, in cost-of-living adjustments, and in pension and wage indexing. It's the price index that follows what consumers actually feel at the checkout.
See Full Mode for the derivation.The inflation rate is the percentage change in the price index:
What this says: Inflation is just how fast the price index is climbing from one period to the next, in percent. If the index went from 100 to 103, prices rose 3%, so inflation is 3%.
Why it matters: Inflation is the rate at which money loses purchasing power. It's the single number central banks try to steer (usually toward about 2%), because both runaway inflation and outright deflation do real damage.
See Full Mode for the derivation.| Feature | CPI | GDP deflator |
|---|---|---|
| Basket | Fixed (consumer goods) | All domestically produced goods |
| Imports | Included (consumers buy them) | Excluded (not produced domestically) |
| New goods | Slow to incorporate | Automatically included |
| Substitution bias | Yes (fixed basket overstates inflation) | No (basket adjusts) |
An economy produces two goods: apples and computers.
| Year 1 (base) | Year 2 | |||
|---|---|---|---|---|
| Price | Quantity | Price | Quantity | |
| Apples | \$1 | 100 | \$1.50 | 80 |
| Computers | \$100 | 10 | \$100 | 15 |
Nominal GDP: Year 1: \$1(100) + \$100(10) = \$1,100. Year 2: \$1.50(80) + \$100(15) = \$1,120.
Real GDP (Year 1 prices): Year 2: \$1(80) + \$100(15) = \$1,580.
GDP deflator (Year 2): \$1,120 / \$1,580 × 100 = 80.7. The price level fell because cheaper computers outweigh more expensive apples.
where $U$ is the number of unemployed, $E$ is the number of employed, and $L = U + E$ is the labor force.
What this says: The unemployment rate is the share of people who want to work and are actively looking but don't have a job, measured against the labor force, not the whole population. Retirees, students, and others not seeking work are left out of both the top and the bottom.
Why it matters: Because it's a share of job-seekers and not of everyone, the rate can fall simply because discouraged workers stop looking, which is why it's read alongside the participation rate rather than on its own.
See Full Mode for the derivation.What this says: The participation rate is the share of working-age people who are in the job market at all, whether they're employed or actively looking. It measures how much of the potential workforce is engaged, not how many have jobs.
Why it matters: It can drop for very different reasons: an aging population retiring, more young people in school, or discouraged workers giving up during a downturn. A falling unemployment rate can hide a falling participation rate, so the two are read together.
See Full Mode for the derivation.Each percentage point of unemployment above the natural rate is associated with about 2% of lost output. The coefficient (2) is an empirical estimate that varies across countries and time periods.
What this says: When unemployment rises 1 percentage point above its "normal" level, the economy loses roughly 2% of its potential output. The relationship is roughly 2-to-1: each point of excess unemployment costs about two points of GDP.
Why it matters: It puts a dollar figure on joblessness. A recession that pushes unemployment 3 points above normal wastes about 6% of what the economy could produce, which adds up to trillions of dollars in a large economy.
See Full Mode for the derivation.An economy has $u_n = 5\%$, potential GDP of $Y^* = \\$10\text{B}$, and actual unemployment of $u = 7\%$.
Output gap: $\frac{Y - Y^*}{Y^*} \approx -2(0.07 - 0.05) = -4\%$
Actual GDP: $Y \approx 0.96 \times \\$10\text{B} = \\$9.6\text{B}$
The economy is producing \$400 million below potential: the cost of 2 percentage points of cyclical unemployment.
A country reports the following data (in billions): Household consumption = \$100, Business investment = \$150, Government purchases = \$100, Exports = \$100, Imports = \$120.
Expenditure approach: $Y = C + I + G + NX = 600 + 150 + 200 + (100 - 120) = \\$130\text{B}$
Component shares: C = 64.5%, I = 16.1%, G = 21.5%, NX = −2.2%.
The income approach would yield the same \$130B by summing wages (\$150B), rent (\$10B), interest (\$10B), profits (\$100B), depreciation (\$10B), and indirect taxes (\$10B).
The production approach sums value added across all industries: agriculture (\$10B), manufacturing (\$150B), services (\$130B) = \$130B.
All three approaches yield identical GDP by the circular flow identity.
| Phase | Description |
|---|---|
| Expansion | Real GDP is rising; employment growing; production increasing |
| Peak | The high point before a downturn |
| Contraction (recession) | Real GDP is falling; employment declining; production decreasing |
| Trough | The low point before a recovery |
Figure 7.2. The business cycle describes short-run fluctuations of GDP around its long-run growth trend. Hover over the GDP line to see the phase at each point in time.
| Classification | Meaning | Examples |
|---|---|---|
| Procyclical | Rises in expansions, falls in recessions | GDP, consumption, investment, employment |
| Countercyclical | Falls in expansions, rises in recessions | Unemployment rate |
| Acyclical | No systematic pattern | Government spending (varies by policy) |
Key regularities:
| Variable | $\sigma_x / \sigma_Y$ | Interpretation |
|---|---|---|
| GDP ($Y$) | 1.00 | Reference |
| Consumption ($C$) | 0.5 | Half as volatile (consumption smoothing) |
| Investment ($I$) | 3.0 | Three times as volatile (amplifier) |
| Hours worked | 0.8 | Nearly as volatile as output |
| Real wages | 0.4 | Relatively smooth |
These regularities aren't abstractions; they were read off real downturns. The economic-history book follows the episodes themselves — the interwar monetary collapse behind the Great Depression, and the 2008 global financial crisis and its aftermath.
The expenditure identity $Y = C + I + G + NX$ can be rearranged to reveal fundamental relationships between saving, investment, and trade.
Private saving: $S_{private} = Y - T - C$
Public saving: $S_{public} = T - G$
National saving: $S = S_{private} + S_{public} = Y - C - G$
From the expenditure identity:
This is the saving-investment identity: the difference between national saving and domestic investment equals net exports. A country that saves more than it invests runs a trade surplus; a country that invests more than it saves must borrow from abroad and runs a trade deficit.
What this says: Every dollar a country earns but doesn't consume or hand to the government is "saved." That saving either finances domestic investment (building factories, houses) or flows abroad as a trade surplus. If a country invests more than it saves, the difference must come from foreign borrowing, which shows up as a trade deficit.
Why it matters: A trade deficit isn't inherently bad; it can mean a country is attracting investment because it has great opportunities. Conversely, a government budget deficit can crowd out trade by absorbing national saving, creating the "twin deficits" pattern.
See Full Mode for the derivation.Adjust the components of GDP and watch the expenditure identity, net exports, national saving, and the S−I=NX identity update in real time.
Figure 7.1. GDP components as a stacked bar. Net exports may be negative, shown below the zero line. The right bar decomposes national saving and investment, verifying $S - I = NX$.
Adjust prices and quantities for two goods. Watch how nominal GDP, real GDP, the GDP deflator, and the inflation rate respond. Notice how inflation can make nominal GDP grow even when real production falls.
Figure 7.3. Comparing nominal GDP (current prices) and real GDP (base-year prices). The gap between them reflects the overall price level change captured by the GDP deflator.
Slide the unemployment rate and watch the output gap and actual GDP respond. Okun's law: each percentage point of unemployment above the natural rate ($u_n$) costs about 2% of potential GDP.
Figure 7.4. Potential GDP vs. actual GDP. The shaded gap represents output lost to cyclical unemployment. When $u = u_n$ (5%), the gap is zero and the economy operates at potential.
The Kaelani Republic is a small island nation with a population of 5 million. We will use Kaelani throughout the macroeconomic chapters as a laboratory for applying theory.
National accounts (Year 1, KD billions): C = 5.0, I = 1.5, G = 2.5, X = 2.0, M = 1.0.
GDP = 5.0 + 1.5 + 2.5 + (2.0 − 1.0) = 10.0 billion KD. GDP per capita: 2,000 KD.
Measurement challenges: Kaelani has a large informal sector (~30% of economic activity). True GDP is likely closer to 13 billion KD.
Labor market: Working-age population: 3.5M. Labor force: 2.8M (LFPR = 80%). Unemployed: 0.28M. Unemployment rate: $u = 10\%$.
Okun's law: If $u_n = 7\%$ and $Y^* = 10.5$B KD, the output gap $\approx -2(0.10 - 0.07) = -6\%$. Predicted actual GDP: \$1.94 \times 10.5 = 9.87$B KD. Measured GDP is 10.0B, suggesting the natural rate estimate is too low, or the Okun coefficient differs for Kaelani.
Maya's lemonade stand revenue of \$123.75 per day (Chapter 2) would count as part of GDP through the expenditure approach, since it is consumption spending by her customers. But if Maya doesn't report her income, it falls into the informal economy and is missed by official statistics. That is exactly the measurement challenge Kaelani faces with its 30% informal sector.
| Label | Equation | Description |
|---|---|---|
| Eq. 7.1 | $Y \equiv C + I + G + NX$ | Expenditure identity |
| Eq. 7.2 | $Y \equiv$ Wages + Rent + Interest + Profits + ... | Income identity |
| Eq. 7.3 | Value added = Revenue − Intermediate inputs | Production approach |
| Eq. 7.4 | Real GDP$_t = \sum P_i^{base} \times Q_i^t$ | Real GDP at base-year prices |
| Eq. 7.5 | GDP deflator = (Nominal GDP / Real GDP) × 100 | GDP deflator |
| Eq. 7.6 | CPI$_t$ = (Cost of basket$_t$ / Cost of basket$_0$) × 100 | Consumer price index |
| Eq. 7.7 | $\pi_t = (P_t - P_{t-1})/P_{t-1} \times 100$ | Inflation rate |
| Eq. 7.8 | $u = U / (U + E)$ | Unemployment rate |
| Eq. 7.9 | $LFPR = L / \text{Working-age population}$ | Labor force participation rate |
| Eq. 7.10 | $(Y - Y^*)/Y^* \approx -2(u - u_n)$ | Okun's law (level form) |
| Eq. 7.11 | $\Delta Y/Y \approx 3\% - 2\Delta u$ | Okun's law (growth form) |
| Eq. 7.12 | $S = I + NX$ | Saving-investment identity |
| Eq. 7.13 | $S - I = NX$ | Trade balance = saving gap |