In the variation of time series, seasonal component and cyclical component are regular component. More and above these there is effect of irregular or random component which is short-term effect.

The element that remains after eliminating the trend T_t, Seasonal component S_t, Cyclical component C_t from the term y_t of the time series is known as random or irregular component and is given by R_t = y_t – (T_t + S_t + C_t).

Random component are subject to natural forces like flood, draught, earthquake, political crisis and random causes like fire, accident, etc. Sometimes it is seen on account of technological innovations.

Random component cannot be controlled nor can be predicted in advance. Hence the variable quantity yt of time series cannot be exactly predicted by studying the time series. Sometimes, effect of random component is temporary and transient. In such situation the stipulated targets of agricultural and industrial production cannot be achieved.