Seasonal Adjustment
Over the year, the size of the Nation's labor force, the levels of
employment and unemployment, and other measures of labor market activity
undergo sharp fluctuations due to seasonal events including changes in
weather, harvests, major holidays, and the opening and closing of schools.
Because these seasonal events follow a more or less regular pattern each
year, their influence on statistical trends can be eliminated by adjusting
the statistics from month to month. These adjustments make it easier to
observe the cyclical, long term trend and other nonseasonal movements in
the series. In evaluating changes in a seasonally adjusted series, it is
important to note that seasonal adjustment is an approximation and initial
adjustment must be based on experience.
Beginning in 1992, BLS introduced publication of seasonally adjusted
labor force data for the 50 States, the
District of Columbia, and Puerto Rico. Beginning in 1996, seasonal
adjustment was extended to estimates for the Los Angeles-Long Beach
metropolitan area and New York City. In 1998, seasonally
adjusted data for census regions and divisions were published.
With the introduction of the LAUS Redesign in 2005, seasonal
adjustment occurs within the model estimation process through the removal
of the seasonal component. The new modeling approach is used in developing
labor force estimates for Census divisions, States, the Los Angeles-Long
Beach-Glendale metropolitan division, and New York City. It was extended to
six new substate areas in 2005. One of these areas was the New
Orleans-Metarie-Kenner, LA metropolitan area, which was subsequently
removed due to various technical problems following Hurricane Katrina.
The remaining five areas are:
- Chicago-Naperville-Joliet, IL metropolitan division
- Cleveland-Elyria-Mentor, OH metropolitan area
- Detroit-Warren-Livonia, MI metropolitan area
- Miami-Miami Beach-Kendall, FL metropolitan division
- Seattle-Bellevue-Everett, WA metropolitan division
Last Modified Date: September 25, 2008
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