The consumer price index is best described as:

The consumer price index (CPI) is the average cost of a basket of goods and services, weighted to represent the purchases of a typical household, and indexed to a reference base period. The inflation rate is a percentage change in a price index such as the CPI. Inflation as measured by the CPI is believed to overestimate the actual increase in the cost of living because it does not account for structural changes such as new goods, quality improvements, or consumers shifting their purchases to lower-priced goods.