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The price level is the average price at which each unit of physical output is sold. A commonly used measure is a consumer price index, which is one particular type of price index. Price indexes are typically constructed to have a relative value of 100 (or 1.00) in a specific year called the base year.

Inflation or the inflation rate is measured by the percentage increase in the price level per year. Similarly, a negative rate of inflation is referred to as deflation.