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Revisions and updates to CPI data : Recalculating seasonal adjustment factors and expenditure weights

Summary:
The FRED Blog has used ALFRED graphs to discuss the regular revisions to employment data and the periodic updates to real gross domestic product data. Here, once again, we tap into ALFRED to discuss revisions and updates to consumer price index (CPI) data. The bars in the ALFRED graph above show the annual CPI inflation rates between 2018 and 2021 using two different vintages of CPI data: before (in red) and after (in blue) the January 2022 revision and update to the CPI data. The differences in annual inflation rates are minimal, so what is involved in those revisions and updates? The revisions are conducted every year and involve adjusting many of the 80,000 individual prices recorded every month for changes in their seasonal patterns. For example, fresh fruit prices are lower

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The FRED Blog has used ALFRED graphs to discuss the regular revisions to employment data and the periodic updates to real gross domestic product data. Here, once again, we tap into ALFRED to discuss revisions and updates to consumer price index (CPI) data.

The bars in the ALFRED graph above show the annual CPI inflation rates between 2018 and 2021 using two different vintages of CPI data: before (in red) and after (in blue) the January 2022 revision and update to the CPI data. The differences in annual inflation rates are minimal, so what is involved in those revisions and updates?

The revisions are conducted every year and involve adjusting many of the 80,000 individual prices recorded every month for changes in their seasonal patterns. For example, fresh fruit prices are lower during harvest on account of the bountiful supply available. The BLS considers these price swings and reports seasonally adjusted price indexes. However, the seasonal changes in prices can be as fickle as the seasonal weather and the corresponding adjustment factors used by the BLS require regular evaluation.

The updates are conducted every two years and involve adjusting the relative weights of goods and services purchased across eight different categories of consumer spending. For example, over the past two years of COVID-19-induced disruptions to regular life, consumers shifted their food purchases away from restaurants towards groceries. The BLS considers those changed patterns by introducing new spending weights in its market basket for goods and services.

Some research shows the impact large-scale and less-frequent revisions and updates to CPI data have on the accurate calculation of consumer price inflation. In that light, the small differences in annual inflation rates across data vintages reflected in the ALFRED graph are a testament to the value of more frequent and smaller-scale updates to CPI data. More accurate data facilitates better decision making, even if the reported inflation rates do not change much.

How this graph was created: Search ALFRED for “Consumer Price Index for All Urban Consumers: All Items in U.S. City Average.” By default, ALFRED shows a graph with two sets of bars: the most recent vintage and the prior vintage. Add additional vintages by using the “Add Line” tab and select the date of the desired vintage from the “or select a vintage” dropdown menu. Change the start date and the end date above the graph to customize the number of data points shown.

Suggested by Diego Mendez-Carbajo.

About FRED Blog
FRED Blog
The Federal Reserve Bank of St. Louis is the center of the Eighth District of the Federal Reserve System. This District includes Arkansas, eastern Missouri, southern Illinois and Indiana, western Kentucky and Tennessee, and northern Mississippi.

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