Measurement problems

For various reasons, there are some difficulties associated with any attempt to express the overall change in prices as one number.

First, an existing basket usually becomes less and less representative over time, as consumers increasingly substitute more expensive goods for cheaper ones. For example, higher petrol prices might lead some people to drive less and buy a higher quantity of other goods instead. Therefore, if the weights are not adjusted, the change in the index may slightly overestimate the “true” price increases. Second, changes in quality are sometimes difficult to incorporate into the price index. If the quality of a product improves over time and the price also rises, some of the change in price is due to the improved quality. Price increases which are due to quality changes cannot be considered as giving rise to inflation, as they do not reduce the purchasing power of money. Changes in quality are commonplace over long periods of time. For example, today’s cars differ considerably from those manufactured in the 1970s, which in turn were very different from those of the 1950s. Statistical offices spend a lot of time making adjustments for quality changes, but by their very nature such adjustments are not easy to estimate. Apart from new varieties of existing goods (e. g. the introduction of new breakfast cereals), an important and difficult subject is the inclusion of new products. For example, after DVD players came on the market, there was an inevitable time lag until they could be captured in price statistics, since information on the market shares, the main distribution channels, the most popular makes, etc., was needed. But if it takes too long to incorporate new products into the price index, the price index fails to fully reflect the actual average price changes that consumers are facing.

In the past, a number of economic studies have identified a small but positive bias in the measurement of national consumer price indices, suggesting that a measured inflation rate of, say, smaller than 1/2 percentage point might in fact be consistent with “true” price stability. For the euro area (i.e. all the EU countries that have adopted the euro as their currency), no precise estimates for such a measurement bias are available. However, one can expect the size of such a possible bias to be rather small for two reasons. First, the Harmonized Index of Consumer Prices (HICP) – this is a harmonized CPI for all euro area countries – is a relatively new concept. Second, Eurostat, the European Commission agency responsible for this area of statistics at the EU level, has attempted to avoid a measurement bias in the HICP by setting appropriate statistical standards.