In statistics relating to national economies, the indexation of contracts also called "index linking" and "contract escalation" is a procedure when a contract includes a periodic adjustment to the prices paid for the contract provisions based on the level of a nominated price index. The purpose of indexation is to readjust contracts to account for inflation.[1] [2] In the United States, the consumer price index (CPI), producer price index (PPI) and Employment Cost Index (ECI) are the most frequently used indexes.[3]