1.3 Descriptive Techniques

These help in classifying the main properties of a time series.
Traditionally time series are analyzed by first decomposition of its components, namely: trends, seasonal effects, cycling effects and irregular (or residues).
These components constitute the sources of variation of a time series.

1.

Seasonal effects: this exhibits variation which is annual in period.

2.

Cyclic effects: time series may exhibit variation in a fixed period due to some other physical causes. may have a period variation in between 5-7 years.

3.

Trend: this is a long term change in mean level.

4.

Irregular fluctuations: after trend seasonal the cyclic variation are removed from a series. We are left with a series of residuals which may or may not be random.

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