Chapter 24 – Measuring a Nation’s Income (Mankiw 10e)

Economics splits into two central branches
- Microeconomics – household & firm decision making; market interaction
- Macroeconomics – economy-wide phenomena: inflation, unemployment, growth
Key identity: Income equals expenditure (every dollar spent by a buyer = income to a seller)
- Example (Active Learning 1)
- Nalah pays James 50 to mow her lawn ➜ Total expenditure ↑ 50; total income ↑ 50
Circular-Flow Diagram (high-level abstraction)
- Shows flows between households and firms
- Four equivalent labels for GDP in the diagram
- Spending
- Revenue
- Factor payments (wages, rent, profit)
- Income
- Factors of production: labor, land, capital, natural resources
- Omits
- Government (taxes & purchases)
- Financial system (savers ↔ borrowers)
- Foreign sector (trade in g&s, assets, currencies)

Formal definition:
- Gross Domestic Product (GDP) = market value of all final goods & services produced within a country during a given period
Dissecting the definition
- “Market value” ➜ priced items only; home production (e.g., own housework) excluded
- “All” ➜ includes any legally sold item; excludes illicit sales & most household production
- “Final” ➜ counts only goods for end users; value of intermediates already contained in final price
- “Goods & services produced” ➜ current production only; covers tangibles (cars) & intangibles (haircuts)
- “Within a country” ➜ territorial, not citizenship test
- “Given period” ➜ standard: quarterly or yearly
Active Learning 2 (market vs. non-market)
- Paid mowing enters GDP; unpaid spousal mowing after marriage does not

National expenditure identity Y = C + I + G + NX
- Y — GDP
- C — Consumption
- I — Investment
- G — Government purchases
- NX — Net exports (Exports − Imports)
Component details
- Consumption (C)
- Household spending on g&s except new housing
- Housing treatment
  - Renters: monthly rent enters C
  - Homeowners: imputed rental value (owner-occupied rent) enters C; purchase price & mortgage payments do not
- Investment (I)
- Business capital (structures, equipment, IP)
- Residential capital (landlord buildings & owner residences)
- Inventory accumulation (produced but unsold)
- Government Purchases (G)
- Local, state, federal spending on g&s
- Excludes transfer payments (Social Security, UI) because nothing is produced
- Net Exports (NX)
- \text{Exports}: foreign spending on domestic output
- \text{Imports}: domestic spending on foreign output
- NX = \text{Exports} - \text{Imports}
U.S. 2021 composition (Table 1)
- Y = \$22.994\text{ trn}
- C 68 %, I 18 %, G 18 %, NX −4 %
Active Learning 3 highlights
- Restaurant dinner ➜ C\uparrow 300; GDP +300
- Imported business phone ➜ I\uparrow 1{,}200, NX\downarrow 1{,}200; GDP unchanged
- Discounted last-year domestic tablet ➜ already counted when produced; resale has no effect on GDP
- Unsold GM cars ➜ C\uparrow 470 m, inventory I\uparrow 30 m; GDP +500 m

Nominal GDP – valued at current-year prices
Real GDP – valued at constant (base-year) prices ➜ controls for price changes
GDP deflator \text{GDP Deflator} = 100 \times \frac{\text{Nominal GDP}}{\text{Real GDP}}
- Index = 100 in base year; tracks price level of all domestically produced g&s
- Inflation rate between t and t+1:
  \%\,\Delta\text{Prices} = \frac{\text{Deflator}{t+1} - \text{Deflator}t}{\text{Deflator}_t} \times 100
Hot-dog & hamburger example (Tables 2–3)
- Base year 2022 ➜ Real GDP 2023 =350, Nominal GDP =600, Deflator =171
Active Learning 4 answers
- 2021 Nominal GDP =167{,}400
- 2022 Real GDP =181{,}000
- 2023 GDP deflator \approx134.4 (inflation relative to 2021 base)
Long-run U.S. Real GDP chart (Figure 2) shows business-cycle recessions (shaded)

Merits
- “Single best measure” of economic capacity
- Higher GDP allows societies to fund healthcare, education, environmental protection, leisure infrastructure
Limitations (Robert Kennedy quote captures intuition)
- Excludes
- Leisure time
- Non-market production (home cooking, volunteer work, DIY repairs)
- Underground/illegal activity
- Environmental degradation
- Quality of social & political institutions; income distribution
Cross-country snapshot (Table 3)
- Positive but imperfect correlation between GDP per capita and
- Life expectancy
- School attainment
- Self-reported life satisfaction (0–10 scale)
Think-Pair-Share reflection
- \$63{,}000/\$630 = 100 × richer is material, market-measured gap, not total well-being gap
- Informal activity (home farming, barter, caregiving) likely larger share of Caribbean output ➜ GDP underestimates it more than for U.S.

Macroeconomics uses GDP statistics as the starting point for analyzing growth, cycles, inflation & policy
Reliable measurement ➜ prerequisite for theory testing & policy design

Y = C + I + G + NX (national expenditure identity)
Nominal GDP: \sum Pt Qt
Real GDP (base year b): \sum Pb Qt
GDP Deflator: 100 \times \dfrac{\text{Nominal GDP}}{\text{Real GDP}}
Inflation Rate based on GDP deflator: \frac{\text{Deflator}{t+1}-\text{Deflator}t}{\text{Deflator}_t} \times 100
Gross National Product (GNP): GDP + income earned by nationals abroad − income earned by foreigners domestically

Ethics & Equity: GDP ignores distribution; growth can accompany widening inequality
Sustainability: GDP treats depletion of natural capital as income; green accounting seeks to correct this
Policy Caution: Overemphasis on GDP may drive governments to prioritize short-term output over health, environment or social cohesion

Link back to Chapter 23 (Production Possibilities & Scarcity): GDP growth shifts the production-possibility frontier outward
Anticipate Chapter 25 (Cost of Living, CPI): GDP deflator covers domestically produced g&s; CPI tracks consumer basket, includes imports
Practice converting nominal ↔ real values; exam problems often mix base-year changes, inventory adjustments, and import leakages
Memorize the expenditure identity and be ready to classify borderline cases (e.g., used goods, transfer payments, intermediate inputs)