The Consumer Price Index (CPI) for food is a component of the all-items CPI. The CPI measures the average change over time in the prices paid by urban consumers for a representative market basket of consumer goods and services. While the all-items CPI measures the price changes for all consumer goods and services, including food, the CPI for food measures the changes in the retail prices of food items only. ERS's monthly update is usually released on the 25th of the month; however, if the 25th falls on a weekend or a holiday, the monthly update will be published on either the 23rd or 24th.
See ERS's report on price forecasting methodology:
How USDA Forecasts Retail Food Price Inflation
This report provides a detailed outline of ERS's forecasting methodology, along with measures to test the precision of the estimates (May 2015).
To read the rest of the story, please go to: USDA ERS
