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Bureau of Labor Statistics > Mass Layoff Statistics > About

Changes to Mass Layoff Statistics Data

Beginning with data for January 2005, BLS is seasonally adjusting six monthly MLS series with the X-12-ARIMA program. Seasonal adjustment is the process of estimating and removing periodic fluctuations caused by events such as weather, holidays, and the opening and closing of schools. The purpose for seasonally 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 will be 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 month’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.

Complete historical series beginning in April 1995 will be available via "Get Detailed MLS Statistics."

Last Modified Date: December 14, 2004