The various reasons or the forces which affect the values of an observation in a time series are the components of a time series. Explain briefly any four components of time series
i) Secular trend, which shows the general tendency of the data to increase or decrease or remain steady over a long time period. The rise and fall may be gradual or steep.
ii) Seasonal variations, variations which operate in a regular and periodic manner over a period of less than a year. These variations have the same or almost the same pattern during a period of 12 months. These variations will be present in a time series if the data are recorded hourly, daily, weekly, quarterly, or monthly.
iii) Cyclic variations, these are oscillatory movements which have a period of oscillation of more than a year. Most of the time series associated with economics and business show some kind of cyclical variations.
iv) Random or Irregular movements, these are fluctuations which are purely irregular or random. The causes of irregular variations are due to accidental situations such as earthquakes, wars, fires, strikes, floods or famine. These fluctuations are unpredictable, unforeseen, uncontrollable and erratic.
Time series is a sequence of well defined data points measured at a constant time interval over a period of time. Hence, it is a sequence of discrete-time data.