as comparable replacements or (2) that could be explicitly quality adjusted by a hedonic or direct cost method.

Commodities and Services (C&S) Survey

A longitudinal survey in which field agents of the Bureau of Labor Statistics (BLS) collect price quotes from sample outlets for items currently included in the CPI.

Commodity analyst

A member of BLS’s CPI team who determines the comparability of disappearing and replacement items that arise in the CPI sample.

Comparison period

The second (often the current) period in the price or cost-of-living comparison.

Conditional cost-of-living index (CCOLI)

The minimal expenditure ratio needed to maintain a given standard of living in the face of changes in the prices of private goods and services, on the assumption that “outside conditions”—the status of the social and physical environment and the provision of goods by the government—remain unchanged.

Consumer demand function

A construct that indicates the relationship between prices and income on one hand and, on the other, the quantity of a good demanded.

Consumer Expenditure Study (CEX)

An annual survey, designed to produce household-level data on both income and consumption, from which the BLS establishes item category (upper-level) expenditure weights.

Consumer substitution

The purchase by consumers of more of one good (that has become relatively cheaper) and less of another (that has become relatively more expensive) in response to a relative price change. See lower-level substitu tion, upper-level substitution.

Cost-of-goods index (COGI)

An index in which a fixed basket of goods is priced each period, calculated as the cost of the basket in the comparison period divided by the cost of the basket in the reference period.

Cost-of-living index (COLI)

An index based on the minimal expenditure ratio needed to maintain a given standard of living (however determined) in the com parison period and the reference period.


The Consumer Price Index, a modified Laspeyres index which tracks the price of 218 categories of goods across 87 primary sampling units in urban areas of the United States.

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