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Time series

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Time series  (TIME series)

When the movement of a demographic variable in time is considered, a demographic time series1 is obtained. It is sometimes possible to decompose a time series into a trend2 around which there are fluctuations3, variations3 (141-1) or deviations3 (141-2). Where such fluctuations tend to recur after certain periods, they are called periodic fluctuations4 or sometimes cyclical fluctuations4, In demography the most common period is a year, and the fluctuations in sub-periods are called seasonal fluctuations5. The fluctuations that remain after trend and periodic fluctuations have been eliminated are called irregular fluctuations6. They may be due to exceptional factors, e. g. to mobilization, or sometimes they are chance fluctuations7 or random fluctuations7.