What compares the prices of a group of selected items each year some earlier year?

The Consumer Price Index (CPI) compares the prices of a selected group of items, known as a "basket of goods," over time, typically measuring changes annually against a base year. It reflects the average change in prices consumers pay for these goods and services, helping to assess inflation and cost of living adjustments. By tracking this index, economists and policymakers can gauge economic trends and make informed decisions.