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Seasonal Adjustment FAQs

What is the difference between seasonally adjusted and not seasonally adjusted data? Why are there two ways to report economic data?
There are two measures used to evaluate changes in economic time series data: seasonally adjusted and not seasonally adjusted. Both measures have distinct advantages for addressing specific issues and both are correct when used appropriately.
What is seasonally adjusted data?
Many economic data series have patterns that tend to occur at the same time each year. Examples include construction employment declining in winter, tourism employment rising in summer, and retail employment peaking in December. Because of such seasonal factors, a mathematical process called seasonal adjustment is sometimes used when analyzing employment statistics to account for these predictable patterns in the raw data in order to help reveal underlying trends.
What is not seasonally adjusted data?
A data series that has not been subjected to the seasonal adjustment process is defined as not seasonally adjusted (also known as non-seasonally adjusted). In other words, the effects of fluctuations due to such factors as season, production cycles, and holidays have not been removed from these data series. Not seasonally adjusted data is the measured value and is considered an actual or raw data series.
When is seasonally adjusted data typically used?
Seasonally adjusted data series are often used for comparisons over time, particularly if two time periods have different seasonal patterns. Any point in time can be compared to any other point in time because seasonal fluctuations have been removed.
When is not seasonally adjusted data typically used?
Not seasonally adjusted data is often used when evaluating shifts or trends over longer periods of time, such as several years.
How are the seasonal adjustment factors determined?
Seasonal adjustments are determined by the US Bureau of Labor Statistics.
What series provides the most accurate comparison between National, State and Local data?
In cases where seasonally adjusted data is only available for the state and nation and not for local areas, the not seasonally adjusted data series should be used in instances where data for local, state and nation are all being compared together.
What DWD programs have seasonally adjusted data series?
The Current Employment Statistics (CES) program has both seasonally adjusted and not seasonally adjusted data available for State and Metropolitan Statistical Area (MSA) employment estimates. The Local Area Unemployment Statistics (LAUS) program has both seasonally adjusted and not seasonally adjusted data available for state labor force and unemployment estimates; local estimates, such as MSAs, counties, or cities, are not seasonally adjusted.



Last updated 11/15/2010

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