ECON1002 · Introductory Macroeconomics
Prices, Inflation & Interest Rates
This chapter measures the price level with the CPI — a fixed-basket, Laspeyres index — and turns it into inflation, then audits the CPI's biases (substitution, quality) and the real costs of inflation, including bracket creep in a non-indexed progressive tax. It closes with the Fisher equation i = r + π, separating the nominal interest rate written in a contract from the inflation-adjusted real return.
It is examined as MCQ calculation: computing inflation and a single item's contribution to it, deflating a nominal value, and applying Fisher to find a real return or an inflation-indexed repayment.
What this chapter covers
- 011. The CPI: cost of a FIXED basket; a Laspeyres (base-year-weight) index
- 022. Inflation: (CPIₜ − CPIₜ₋₁)/CPIₜ₋₁ × 100; quarterly vs year-ended
- 033. One item's contribution to inflation = expenditure share × its % price change
- 044. CPI biases: substitution bias, quality bias, heterogeneous preferences (CPI overstates true cost of living)
- 055. Costs of inflation: eroded purchasing power, menu & shoe-leather costs, redistribution, bracket creep
- 066. Deflating vs indexing: real value = nominal / (CPI/100); indexing keeps real values constant
- 077. Fisher equation i = r + π ⇒ r = i − π; nominal vs real interest; unanticipated inflation hurts creditors
- 088. Deflation & the zero lower bound: with i near 0, deflation forces the real rate UP
Contribution of one item to CPI inflation, and the Fisher real rate
- 1 mark(a) A category's contribution to inflation is its expenditure share times its own % price change: 0.08 × 50% = 4 percentage points.
- 1 mark(b) Indexing protects the REAL return, so compound the real return with inflation using exact Fisher: (1 + i) = (1 + r)(1 + π) = 1.08 × 1.05 = 1.134, i.e. i = 13.4%.
- 1 markApply the gross factor to the principal: repayment = 200 × 1.134 = $226.80 (the approximation i ≈ r + π = 13% gives $226, also acceptable).
Key terms
- Consumer Price Index (CPI)
- The cost of a fixed basket of goods and services bought by a typical household, expressed as an index. Because the basket (the quantity weights) is held at base-year levels, it is a Laspeyres index.
- Inflation rate
- The percentage change in the price index over a period: (CPIₜ − CPIₜ₋₁)/CPIₜ₋₁ × 100. 'Year-ended' inflation compares the index to the same quarter a year earlier; 'quarterly' compares consecutive quarters.
- Substitution & quality bias
- Because the CPI fixes the basket, it overstates the true rise in the cost of living: it ignores consumers switching away from goods that became relatively dear (substitution bias) and improvements in product quality over time (quality bias).
- Bracket creep
- In a progressive, non-indexed income tax, inflation pushes nominal incomes into higher tax brackets even when real income is unchanged, raising the average tax rate. It is a hidden cost of inflation that lowers real after-tax income.
- Fisher equation
- i = r + π: the nominal interest rate equals the real rate plus expected inflation (so r = i − π). The nominal rate is fixed in the contract; the real rate is the inflation-adjusted return, and unanticipated inflation transfers wealth from lenders to borrowers.
- Zero lower bound (ZLB)
- Nominal interest rates cannot fall much below zero. Because r = i − π, deflation (negative π) then forces the real rate UP even with i at zero, which discourages borrowing and investment and is hard for monetary policy to offset.
Prices, Inflation & Interest Rates FAQ
How is inflation examined in ECON1002?
As short MCQ calculation: compute an inflation rate from two CPI values, find a single item's contribution to inflation (share × % price change), deflate a nominal income to real terms, or apply the Fisher equation to find a real return or an inflation-indexed repayment. The arithmetic is light but sign- and decimal-sensitive, so practise the setups.
Why does the CPI overstate the true cost of living?
Because it holds the basket fixed. When a good becomes relatively expensive, households substitute toward cheaper alternatives, but the fixed-basket CPI keeps buying the now-dear good (substitution bias). It also struggles to strip out quality improvements (quality bias) and assumes everyone buys the same basket (heterogeneous preferences). All three push measured CPI inflation above the true rise in living costs.
What is the difference between deflating and indexing?
Deflating converts a nominal value into real terms after the fact: real value = nominal value / (CPI/100), letting you compare purchasing power across years. Indexing builds inflation protection into a contract in advance, so a pension or wage rises automatically with the CPI to keep its real value constant. Deflating is measurement; indexing is policy.
Why does unanticipated inflation hurt lenders?
Loan contracts fix the nominal rate i. The real return is r = i − π, so if inflation π turns out higher than expected, the lender is repaid in dollars worth less than anticipated and r falls — the borrower gains, the lender loses. This is why lenders demand an inflation premium and why index-linked contracts, which adjust the nominal repayment for actual inflation, lock in the real return.
Exam move
Separate the three skills and drill each: (1) inflation arithmetic — practise CPI-to-inflation and the contribution formula (share × % price change), being careful to use the decimal share and the % change, not the level; (2) deflating — convert nominal to real with real = nominal / (CPI/100) and interpret the direction; (3) Fisher — memorise i = r + π and be ready to compound (1+r)(1+π) when precision is required, and to read whether the question gives you the real or nominal rate. Keep a one-line note of each cost of inflation (menu, shoe-leather, redistribution, bracket creep) for the conceptual MCQ, and rehearse the ZLB logic (deflation forces the real rate up) since it is a favourite catch.
