Both RPI and CPI measure changes in prices, but track slightly different baskets of goods and services and use different methods to calculate inflation.

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These shorter studies have been based on methods that are very different from the Harvard-OSU research, but in the 2, 000 years that they overlap, the results have been basically the same.

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But in fact, the main reason for the two indices rising at different rates is because they use different arithmetical methods for calculating average prices.

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