In January of each year, the Federal Reserve Bank of Philadelphia revises historical data for the Manufacturing Business Outlook Survey. Because survey responses are characterized by seasonal patterns, new seasonal factors are calculated annually based on the addition of a complete year of data.

While this year's revisions altered levels of the indexes for most months, the direction of month-to-month changes in most series was similar (see the charts and links to the revised historical data below).

For the current general activity index, the average absolute difference between the originally released data and the revisions was 2.2 points. Revisions to the current general activity index for 2019 also removed the previous high point of the series in July; the index that month was revised down 5.2 points (see Chart 1). The index trended down over the last 5 months of the year. For December 2019, the index was revised up slightly, from 0.3 to 2.4.

Seasonal adjustments were based on the U.S. Census Bureau's Census X-12 program, and seasonal factors for the 12 months of 2020 are being projected using the X-12-ARIMA method. Adjustments were calculated based on the most recent 50 years of data.

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