BEO6600 · Business Economics
Measuring the Macroeconomy
This session turns from single markets to the whole economy, starting with measurement. Gross Domestic Product (GDP) is the market value of all final goods and services produced within a country in a period; because every dollar spent is a dollar of income, we measure it by adding up spending with the expenditure identity Y = C + I + G + NX. To separate real production from price changes, we compare nominal GDP (output at current prices) with real GDP (output at base-year prices) and compute the GDP deflator = (nominal ÷ real) × 100. The Consumer Price Index (CPI) tracks the cost of a fixed basket in five steps, and the inflation rate is the percentage change in the CPI — dividing by the earlier year. The session closes conceptually with the quantity theory of money (MV = PY), monetary neutrality and the Fisher equation. This is the most calculation-rich macro topic and is on the closed-book exam.
What this chapter covers
- 017.1 What GDP measures (final goods; final vs intermediate)
- 027.2 The expenditure approach: Y = C + I + G + NX
- 03Edge cases: new housing in I, transfers excluded from G, NX can be negative
- 047.3 Real vs nominal GDP and the GDP deflator
- 057.4 The Consumer Price Index (CPI) in five steps; the inflation rate
- 067.5 CPI vs the GDP deflator; why the CPI overstates inflation
- 077.6 Indexation and the real interest rate
- 087.7 The quantity theory of money, monetary neutrality, Fisher (conceptual)
Worked example: GDP, the deflator and the inflation rate
- +1(a) Net exports first: NX = exports − imports = 90 − 110 = −$20bn (a trade deficit subtracts from GDP).
- +1Add the four components: Y = C + I + G + NX = 600 + 150 + 220 + (−20) = $950bn.
- +1(b) GDP deflator = (nominal ÷ real) × 100 = (600 ÷ 480) × 100 = 125.
- +1Interpret: nominal GDP rose 50% but real output rose only 20% ($400 → $480); the deflator of 125 says the price level is 25% above the base year — that 25% is the price part of the nominal jump.
- +1(c) CPI = (basket cost ÷ base cost) × 100. Base = 100; Year 2 = 48/40 × 100 = 120; Year 3 = 54/40 × 100 = 135.
- +1Inflation Year 2 → 3 = (135 − 120) ÷ 120 × 100 = 12.5% — divide by the earlier year (120), not 100 and not 135.
Key terms
- Gross Domestic Product (GDP)
- The market value of all final goods and services produced within a country in a given period. Final goods only (to avoid double-counting), produced now (not resales), within the country (a geographic measure). For the whole economy, income equals expenditure, since every sale is someone's income.
- Expenditure identity (Y = C + I + G + NX)
- The way GDP is measured: consumption (C, excludes new housing) plus investment (I, which is where new housing sits) plus government purchases (G, excludes transfer payments) plus net exports (NX = exports − imports, which can be negative).
- Real vs nominal GDP
- Nominal GDP values output at current prices; real GDP values the same output at constant base-year prices, so any change in real GDP is a change in quantities. Real GDP is the better gauge of production and material welfare because it strips out price changes.
- GDP deflator
- A measure of the price level equal to (nominal GDP ÷ real GDP) × 100; in the base year it equals 100. It isolates the price part of a change in nominal output — a deflator of 125 means the price level is 25% above the base year.
- Consumer Price Index (CPI)
- An index tracking the cost of a fixed basket of goods bought by a typical consumer, compiled in Australia by the ABS. CPI = (basket cost in the year ÷ base-year cost) × 100, and the inflation rate is the percentage change in the CPI, dividing by the earlier year.
Measuring the Macroeconomy FAQ
What counts in GDP and what is left out?
GDP counts the market value of final goods and services produced now, within the country. It excludes intermediate goods (counted inside the final good, to avoid double-counting), resales of second-hand goods and financial assets (not current output), most home production that never reaches a market, and illegal transactions. Two classic traps: a government transfer like a pension is not in G (it buys no current output), and a newly built house counts as investment (I), not consumption.
What is the difference between nominal and real GDP, and where does the deflator come in?
Nominal GDP values output at current prices, so it rises when either quantities or prices rise. Real GDP values output at constant base-year prices, so it changes only when quantities change — it is the better measure of production. The GDP deflator = (nominal ÷ real) × 100 separates the two: it tells you how much of a nominal change was price rather than output, and it equals 100 in the base year.
How do I compute the inflation rate from the CPI?
First build the CPI: CPI = (basket cost in the year ÷ base-year cost) × 100. Then the inflation rate between two years is (later CPI − earlier CPI) ÷ earlier CPI × 100. The denominator is the earlier (starting) year's index — not 100, and not the later year. Going from a CPI of 120 to 135 gives 12.5%, not 11.1% or 15%; prices still rose, just more slowly than before (disinflation, not deflation).
How does the CPI differ from the GDP deflator?
Both measure the price level but cover different baskets. The CPI tracks goods consumers buy and includes imports, with a basket fixed (updated periodically). The GDP deflator covers all output produced domestically, excludes imports, and changes with current output. They generally move together but can diverge — a jump in imported fuel prices lifts the CPI but not the deflator. The CPI also tends to overstate inflation because of substitution bias, new goods and unmeasured quality change.
Exam move
This is the most numeric macro session, so get the arithmetic clean and exact. For GDP, split spending into C, I, G, NX and watch the edge cases: new housing is investment, transfers are out of G, and NX is the only term that can be negative. For real vs nominal, remember nominal uses current prices and real uses base-year prices, then deflator = (nominal ÷ real) × 100. For the CPI, build the fixed basket's cost each year, index it against the base year, and compute inflation by dividing the change by the earlier year — the most common slip is using the wrong denominator. The quantity theory (MV = PY), monetary neutrality and the Fisher equation are tested conceptually: explain the chain 'more money → lower value of money → higher prices', don't solve for a number.
