The Consumer Price Index (CPI) is a measure of the average change over time in the prices paid by urban consumers for a market basket of consumer goods and services. It is calculated and published monthly by the U.S. Bureau of Labor Statistics (BLS) and is the most widely used measure of inflation. The CPI reflects spending patterns for each of two population groups: all urban consumers and urban wage earners and clerical workers. The market basket includes everything from food items to automobiles to rent. The CPI is constructed using a set of interlocking surveys, and it is fundamentally a measure of price change. The CPI is used by policy makers to understand and analyze the economy, and it provides information about price changes in the nations economy to government, business, labor, and private citizens. The CPI is also used as a deflator for other economic indicators, including retail sales.