Basket of Goods

A basket of goods is a representative set of products and services, each given a weight, whose combined cost is measured repeatedly to track changes in prices. Statistical agencies use it to compile price indices such as the consumer price index, which in turn measure inflation and the cost of living. The basket is meant to reflect what a typical household buys, from food and rent to transport, clothing, energy and phone bills.

The basket is at the centre of how central banks judge price stability, how pensions and benefits are uprated, and how wages and contracts are indexed. It is also used in international comparisons, for example in purchasing power parity calculations, and in informal measures such as The Economist's Big Mac index. The term is distinct from a currency basket, which is a weighted mix of currencies used to set or track exchange rates.

Imagine writing a shopping list of everything your household buys in a typical month: bread, milk, petrol, rent, a haircut, a streaming subscription. Every month you go to the same shops and price the same list, without changing it. If the whole list cost $1,000 last year and costs $1,040 this year, your cost of living has gone up by 4%.

A national statistics office does the same thing on a huge scale. It sends people to collect hundreds of thousands of prices, gives more weight to items people spend more on, and adds it all up. The result tells the country how quickly prices are rising and how far a pay packet stretches.

Statistical agencies follow broadly similar steps:

• Choosing items. Household spending surveys show what people buy. Agencies then choose representative items within categories, such as a specific size of loaf in "bread and cereals".
• Setting weights. Each category is weighted by its share of total household spending, so housing and transport count for much more than, say, stamps.
• Collecting prices. Prices are gathered regularly from shops, websites and service providers across the country, increasingly using scanner and web data.
• Adjusting for quality. When products change, agencies apply hedonic adjustment and other methods so that a better phone at the same price is not recorded as no change.
• Updating the basket. Items and weights are refreshed, often annually, to reflect new products and changing habits.

In the United Kingdom, the Office for National Statistics publishes its annual basket changes, which attract attention as a snapshot of shifting tastes; in the United States, the Bureau of Labor Statistics compiles the CPI.

A basic fixed-basket price index, known as a Laspeyres index, compares the cost of the base-period basket at current prices with its cost at base prices:

• $p_t$ is the price of each item in the current period.
• $p_0$ is the price of each item in the base period.
• $q_0$ is the quantity of each item in the base-period basket.

Suppose a simple basket contains 10 loaves of bread and 4 cinema tickets. In the base year bread costs $2 and tickets $10, so the basket costs $10 \times 2 + 4 \times 10 = 60$. A year later bread costs $2.20 and tickets $11, so the same basket costs $10 \times 2.2 + 4 \times 11 = 66$. The index is $66 \div 60 \times 100 = 110$, meaning prices for this basket rose 10% over the year.

Many central banks set inflation targets based on a basket-derived index, often around 2% a year, and adjust monetary policy when measured inflation moves away from the target. Governments use the same indices to uprate tax thresholds, pensions and welfare payments, and to issue inflation-linked bonds. Employers and unions refer to them in wage negotiations, and landlords and suppliers use them in contracts through a cost of living adjustment or indexation clause. Economists also compare basket indices with the broader GDP deflator, which covers all goods and services produced rather than those bought by households.

A basket is an average and may not match any individual household. Renters, homeowners, pensioners and families with young children face different mixes of prices, so their personal inflation can differ widely from the headline figure. Fixed baskets can overstate inflation because people switch to cheaper items when prices rise, a problem known as substitution bias; chained indices that update weights more often reduce it. New products, quality changes and the treatment of housing costs are persistent sources of debate. Some crypto supporters argue that official baskets understate the loss of a currency's purchasing power, but such claims usually rely on narrower or selected sets of prices rather than a representative basket.

• US Bureau of Labor Statistics: Consumer Price Index
• Office for National Statistics: Inflation and price indices