information:extraction, information:classification, structural:expansion, structural:summarization, structural:reformatting
Overview

The index is usually computed monthly, or quarterly in some countries, as a weighted average of sub-indices for different components of consumer expenditure, such as food, housing, shoes, and clothing, each of which is, in turn, a weighted average of sub-sub-indices. At the most detailed level, the elementary aggregate level (for example, men's shirts sold in department stores in San Francisco), detailed weighting information is unavailable, so indices are computed using an unweighted arithmetic or geometric mean of the prices of the sampled products. (However, the growing use of barcode scanner data is gradually making weighting information available even at the most detailed level.) These indices compare prices each month with prices in the price-reference month. The weights used to combine them into the higher-level aggregates and then into the overall index relate to the estimated expenditures during the preceding whole year of the consumers covered by the index on the products within its scope in the area covered. Thus, the index is a fixed-weight index but rarely a true Laspeyres index since the weight-reference period of a year and the price-reference period, usually a more recent single month, do not coincide.