Revision of Seasonally Adjusted Mass Layoff Statistics Data
At the end of each calendar year, BLS updates the seasonal adjustment
factors to incorporate the data for that year and revises the historical
series for the prior four years. This year, seasonally adjusted data for
January 2008-November 2012 were revised. The revised data replace the
previously published seasonally adjusted data and are available on the Web
site's time series database. The tables below summarize the changes
resulting from these revisions.
BLS seasonally adjusts six monthly MLS series using the X-12-ARIMA
program. Seasonal adjustment is the process of estimating and removing
periodic fluctuations caused by events such as weather, harvests,
holidays, and the opening and closing of schools. The purpose for seasonal
adjustment is to make it easier to observe fundamental changes in the
level of the series, particularly those associated with general economic
expansions and contractions. The method of concurrent seasonal adjustment
is performed monthly in order to use all available data, including the
current month.
Prior adjustments are applied to the series to adjust the original data
for differences in the number of weeks used to calculate monthly data. As
weekly unemployment insurance claims filings are aggregated to form
monthly data, a particular monthÂ’s value could be calculated with five
weeks of data in one year and four weeks in another. This can seriously
distort the seasonal factors if ignored in the seasonal adjustment
process. These effects are modeled in the X-12-ARIMA program and
permanently removed from the final seasonally adjusted series.
In addition, large, unexpected, and rare events such as Hurricane
Katrina can cause a time series to deviate from its expected patterns.
When these types of events occur, changes are made to the MLS seasonal
adjustment procedure through the use of intervention variables to keep the
seasonal factors from becoming seriously distorted.
January 2008-November 2012 Seasonal Adjustment Changes Due to
Revision
- Total Mass Layoff Events and Initial Claims (PDF)
- Private Nonfarm Mass Layoff Events and Initial Claims (PDF)
- Manufacturing Mass Layoff Events and Initial Claims (PDF)
Last Modified Date: January 25, 2013
|
