Consumer Price Index
The set of products for which the index is intended to measure the price changes. The scope of a CPI (Consumer price index) will generally be defined in terms of a designated set of consumption goods and services purchased by a designated set of households. In practice, certain goods and services or households may have to be excluded because it is too difficult, time-consuming or costly to collect the relevant data on expenditures or prices: for example, illegal expenditures. The coverage of an index denotes the actual set of products included, as distinct from the intended scope of the index.
International Labour Organization (ILO), International Monetary Fund (IMF), Organisation for Economic Co-operation and Development (OECD), Statistical Office of the European Communities (Eurostat), United Nations (UNECE), The World Bank, Consumer Price Index Manual: Theory and Practice, Geneva, August 2004