GDP & Measurement
Packet / Part III · Macroeconomics
17

GDP & Measurement

Class 17 · Chapter 17 Final
If you remember one thing

GDP is the market value of final goods and services newly produced in a country in a period — and production = income = spending, so the same number can be measured three ways. Real GDP fixes prices at the base year and lets quantities move.

Every word of the definition is load-bearing

Final
Not intermediate — otherwise you double count.
Newly produced
Not resales.
In a country, in a period
Geography and time bound the measure.

Three ways to measure the same number

Expenditure
Y = C + I + G + NX. The one you will use. Shares: C 65–70%, I 15–20%, G 15–20%, NX about −3%.
Production (value added)
Follow goods through each stage.
Income
Labor income plus capital income.
Anchor numbers
US GDP ≈ $30 trillion, population 340 million, so GDP per person ≈ $88,000.

Real versus nominal

Nominal GDP2022 = Σ Pi,2022 · Qi,2022
Real GDP2022 (2012 base) = Σ Pi,2012 · Qi,2022Nominal = current dollars. Real = adjusted for price changes, measured in goods and services rather than dollars. Real GDP answers: what would this year's output be worth at base-year prices?
growth of X = (Xt − Xt−1) / Xt−1 × 100Applied to real GDP, this is the growth rate of the economy.

Comparing across countries

Currency units break down across space as well as time. China's 2024 nominal GDP was ¥134,908 billion, the US's $29,298 billion. Market exchange rates mislead too: non-traded goods are cheaper in poorer countries. So the IMF uses purchasing power parity "international dollars" — China $38.2 trillion, US $29.3 trillion for 2024. On a PPP basis China's economy is larger; at market exchange rates it is not. Knowing why both are true is the point.

Potential output

Y*/POP = (N*/POP) × (Y*/N*)Normal output per person = normal employment-to-population ratio × normal output per worker. Productivity depends on capital per worker K*/N* and technology T.
Y*
Output when resources are used at normal rates. Edwards: a better name is "normal output" — not a ceiling, since Y can exceed it temporarily.
Three determinants
Labor, capital, technology. Capital includes physical capital, infrastructure and human capital. Technology means production techniques, management techniques, economic institutions and culture.

Rules that earn points

  1. Write Y = C + I + G + NX before answering anything about GDP composition.
  2. If prices are involved, say explicitly whether you are in real or nominal terms.
  3. For cross-country comparisons, name PPP and say why market exchange rates mislead.
  4. For long-run questions, decompose into employment ratio, capital per worker, technology.
Traps
  • Counting intermediate goods or resales in GDP.
  • Using current-year prices for real GDP. Real GDP holds prices fixed at the base year.
  • Treating potential output as a hard maximum. Y can exceed Y* in a boom.
Unit 17 quiz4 MCQ · 2 FRQ · ~12 min
MCQ 12 pts

With 2012 as the base year, real GDP for 2022 equals:

  • AΣ Pi,2022 · Qi,2022
  • BΣ Pi,2012 · Qi,2022
  • CΣ Pi,2022 · Qi,2012
  • DΣ Pi,2012 · Qi,2012
Answer

B — base-year prices times current-year quantities.

Real GDP fixes prices and lets quantities move, so it answers "what would 2022 output have been worth at 2012 prices?"

C is the trap, and it is the mirror image: fixing quantities and letting prices move is how you build the CPI, not real GDP. A is nominal GDP.

MCQ 22 pts

China's 2024 GDP is about $38.2 trillion on one measure and below the US's $29.3 trillion on another. The reason is:

  • AChina's official statistics use a different base year
  • BNon-traded goods are cheaper in China, so PPP international dollars value its output higher than market exchange rates do
  • CThe larger figure is nominal and the smaller is real
  • DThe larger figure includes intermediate goods
Answer

B — purchasing power parity versus market exchange rates.

Converting yuan at market rates understates what that output actually buys, because services and other non-traded goods cost less in poorer countries. PPP "international dollars" correct for this. On a PPP basis China's economy is larger; at market exchange rates it is not.

C is the trap — confusing the real/nominal distinction (across time) with the PPP problem (across space). Both are price adjustments, but they answer different questions.

MCQ 32 pts

Which of the following counts in this year's US GDP?

  • AA 2019 used car sold this year by one household to another
  • BSteel sold by a mill to a carmaker to be built into a new car
  • CA newly built car sold to a household
  • DShares of stock bought this year
Answer

C — the newly built car.

It is final and newly produced — both requirements of the definition.

B is the trap: the steel is real, newly produced output, but it is an intermediate good. Its value is already inside the car's price, and counting both double counts. A is a resale, and D is a financial transfer, not production.

MCQ 42 pts

Potential output Y* is best described as:

  • AThe maximum output the economy is physically capable of producing
  • BThe output produced when resources are used at normal rates, which actual output can temporarily exceed
  • CReal GDP in the base year
  • DThe output level at which inflation is zero
Answer

B — normal output, not a ceiling.

Edwards says a better name would be "normal output." In a boom Y can sit above Y*.

A is the trap, and the word "potential" invites it. Treating Y* as a hard maximum makes the whole short-run chapter incoherent, since booms are defined by Y > Y*.

FRQ 16 pts

An economy produces only bread and books. In 2012 bread was $2 a loaf with 100 loaves produced, and books were $20 each with 10 produced. In 2022 bread was $3 with 120 loaves, and books were $25 with 12 produced. Taking 2012 as the base year, compute nominal GDP in 2022, real GDP in 2022, and the growth rate of real GDP from 2012 to 2022.

Show each product before summing. Give the growth rate as a percentage, and say in one sentence why it differs from nominal growth.
Model answer
Nominal GDP2022 = ($3 × 120) + ($25 × 12) = 360 + 300 = $660
Real GDP2022 = ($2 × 120) + ($20 × 12) = 240 + 240 = $480

In the base year nominal and real GDP coincide: ($2 × 100) + ($20 × 10) = 200 + 200 = $400.

Real growth = (480 − 400) / 400 × 100 = 20%

Nominal GDP grew from $400 to $660, which is 65%. The gap is pure price change: real GDP holds 2012 prices fixed, so only the extra 20 loaves and 2 books count.

What earns the points
  • Base-year prices multiplied by current-year quantities for real GDP — the single thing being tested.
  • Both products shown separately before summing.
  • Recognising that base-year real GDP equals base-year nominal GDP ($400).
  • The percentage-change formula applied to real, not nominal, figures.
  • One sentence attributing the 65% versus 20% gap to price increases.
FRQ 24 pts

Write the decomposition of potential output per person and explain what determines each piece.

Give the identity, then one line per term. Name the three key determinants of potential output.
Model answer
Y*/POP = (N*/POP) × (Y*/N*)

N*/POP is the normal employment-to-population ratio — demographics and labor force participation. Y*/N* is normal average labor productivity, which depends on capital per worker K*/N* and on technology T.

So the three key determinants of potential output are labor, capital and technology. Capital includes conventional physical capital, infrastructure and human capital. Technology is broad: production techniques, management techniques, economic institutions and culture.

What earns the points
  • The identity written as a product of two ratios, with starred (normal) variables.
  • Naming all three determinants: labor, capital, technology.
  • Unpacking capital to include infrastructure and human capital, not just machines.
  • Unpacking technology beyond machinery to include economic institutions and culture.