Definition: Causes of the seasonality

National accounts

There are at least four, or totally distinct, classes of causes of seasonal fluctuations in economic data:
 - calendar;
 - timing decisions;
 - weather;
 - expectation.
These four groups may be thought of as basic causes. They are not always easily distinguishable, may often merge together and the list of basic causes may not be complete. Some series may have seasonal components which are only indirectly due to these basic causes.
Handbook on quarterly national accounts, 1999 Edition, Eurostat, p.200-201

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