The Consumer Price Index (CPI) is the official measure of inflation of consumer prices that examines the weighted average of prices of a basket of consumer goods and services. The CPI Index is used to track price changes associated with the cost of living. In the commercial property market leases are often granted with rent reviews occurring by reference to either the Consumer Prices Index, or more commonly, the Retail Prices Index. The biggest difference between CPI and RPI is in the area of mortgage payments, which are excluded from the CPI but included in the RPI. The CPI was first introduced in 1996 and since 2003 it has replaced the RPI as UK inflation target.