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This statistic shows the 12-month percent change in the chained consumer price index in the U.S. The data represents U.S. city averages. The base period was December 1999=100. The chain weighted CPI incorporates the average changes in the quantity of goods purchased, along with standard pricing effects. This allows the chain weighted CPI to reflect situations where customers shift the weight of their purchases from one area of spending to another. In April 2012, prices went up by 2.1 percent compared to April 2011.