Cost escalation is defined as changes in the cost or price of specific goods or services in a given economy over a period. This is similar to the concepts of inflation and deflation except that escalation is specific to an item or class of items (not as general in nature), it is often not primarily driven by changes in the money supply, and it tends to be less sustained. While escalation includes general inflation related to the money supply, it is also driven by changes in technology, practices, and particularly supply-demand imbalances that are specific to a good or service in a given economy. For example, while general inflation (e.g., consumer price index) in the US was less than 5% in the 2003-2007 time period, steel prices increased (escalated) by over 50 ecause of supply-demand imbalance. Cost escalation may contribute to a project cost overrun but it is not synonymous with it.