The Economist explains

What is a consumer price index?

A measure of inflation, and a tool to guide central bankers

A basket of staple food items at an Iceland Foods Ltd. supermarket in Christchurch, UK, on Wednesday, June 15, 2022. "Britain's cost-of-living crisis -- on track to big the biggest squeeze since the mid-70s -- will continue to worsen before it starts to ease at some point next year," said Jack Leslie, senior economist at the Resolution Foundation, a research group campaigning against poverty. Photographer: Chris Ratcliffe/Bloomberg via Getty Images
Image: Getty Images

INFLATION HAS DOGGED societies for centuries. Attempts to measure it properly began in earnest in the 20th century. In 1914 the British government calculated a “working-class cost of living index” to help guide adjustments to the wages of essential workers during the first world war. America’s Bureau of Labour Statistics (BLS) published inflation measures for 32 cities in 1919, and followed up with a national index in 1921. How do such consumer price indices work—and how have they changed over the years?

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