Index-number practice under conditions of hyperinflation —with particular reference to Peru

The Consumer Price Index (CPI) is a summary, by means of a single number, of a changing relationship between commodities and consumers. Under normal conditions there are stabilities that maintain usual practice with the CPI as a social institution which is adequate for the needs it is designed to meet. Under extreme conditions, important changes take place that cannot be accounted by means of the CPI, or any single number. It may be necessary to monitor such changes on a regular basis. A review of essentials about the CPI will put the concept in a framework for a response to this need.