Measuring Inflation: The Consumer Price Index (CPI)

What is Inflation?

• Inflation is a sustained increase in the general price level of goods and services in an economy over a period of time.
• It represents a reduction in the purchasing power per unit of money – a loss of real value in the medium of exchange and unit of account within the economy.
• Price stability, or low inflation, is a key macroeconomic goal for Australia. The RBA targets an average inflation rate of 2-3% per year, over the economic cycle.

KEY TAKEAWAY: Inflation erodes purchasing power. The RBA targets 2-3% average inflation.

The Consumer Price Index (CPI)

• The Consumer Price Index (CPI) is the primary measure of inflation in Australia. It measures the quarterly changes in the retail prices of a fixed basket of goods and services that represent a high proportion of expenditure by metropolitan households.
• Compiled by the Australian Bureau of Statistics (ABS).
• The CPI is a weighted average of price changes, reflecting the relative importance of different items in household spending.

CPI Basket of Goods and Services

The CPI basket includes a wide range of goods and services, categorized into groups such as:

• Food and non-alcoholic beverages
• Alcohol and tobacco
• Clothing and footwear
• Housing
• Household contents and services
• Health
• Transport
• Communication
• Recreation and culture
• Education
• Insurance and Financial Services

Calculating the CPI

1. Base Year: A base year is chosen, and the CPI is set to 100 for that year.
2. Price Survey: The ABS collects price data for the goods and services in the CPI basket each quarter.
3. Weighting: Each item in the basket is assigned a weight based on its proportion of average household expenditure.

4. Calculating Index: The CPI for a given period is calculated as:

   $$
   \text{CPI} = \frac{\text{Cost of basket in current year}}{\text{Cost of basket in base year}} \times 100
   $$

5. Inflation Rate: The inflation rate is the percentage change in the CPI from one period to the next:

   $$
   \text{Inflation Rate} = \frac{\text{CPI}{\text{current}} - \text{CPI}{\text{previous}}}{\text{CPI}_{\text{previous}}} \times 100
   $$

STUDY HINT: Practice calculating the CPI and inflation rate using sample data.

Headline vs. Underlying (Core) Inflation

• Headline Inflation: The headline CPI measures the price changes of all goods and services in the CPI basket. It is the raw, unadjusted measure of inflation.
• Underlying (Core) Inflation: Underlying inflation attempts to remove the impact of volatile or one-off price changes that can distort the headline rate. It provides a more accurate picture of persistent inflationary pressures in the economy.

Why Use Underlying Inflation?

• Headline inflation can be affected by short-term factors, such as:
  • Seasonal price fluctuations (e.g., fruit and vegetables)
  • Changes in government policies (e.g., taxes, subsidies)
  • Global events (e.g., oil price shocks)
• Underlying inflation provides a better indication of the trend in inflation and helps policymakers make informed decisions about monetary policy.

Measures of Underlying Inflation

The ABS and RBA use several measures of underlying inflation, including:

• Trimmed Mean: The trimmed mean CPI excludes the 15% of items with the largest price increases and the 15% with the smallest price increases (or largest decreases).
• Weighted Median: The weighted median CPI is the price change at the midpoint of the distribution of price changes, weighted by their expenditure shares.

EXAM TIP: Explain the difference between headline and underlying inflation and why policymakers focus on underlying measures.

Impact of Volatile Price Changes

• A large increase in the price of a volatile item, such as fruit and vegetables due to a weather event, will have a significant impact on the headline rate of inflation.
• However, it will have a smaller impact on the underlying rate of inflation because the trimmed mean and weighted median measures remove or down-weight these volatile items.

COMMON MISTAKE: Confusing headline and underlying inflation. Remember that underlying inflation is designed to be a more stable measure.

Interpreting Inflation Data

• When analyzing inflation data, it is important to consider both the headline and underlying rates.
• A large difference between the two rates may indicate that volatile price changes are distorting the overall picture of inflation.
• Policymakers typically focus on underlying inflation when making decisions about monetary policy, as it provides a better indication of the trend in inflation.

VCAA FOCUS: VCAA often asks students to interpret graphs showing trends in headline and underlying inflation rates and to explain the reasons for differences between the two.

Other Measures of Inflation

• Producer Price Index (PPI): Measures changes in the prices of goods and services sold by producers.
• Wage Price Index (WPI): Measures changes in the price of labour.
• House Price Index (HPI): Measures changes in the prices of residential properties.
• Pensioner and Beneficiary Living Cost Index (PBLCI): Measures price increases specifically affecting pensioners.

REMEMBER: CPI measures consumer prices; PPI measures producer prices; WPI measures wage prices.