Statistical data which is recorded with its time of occurrence is called a time series. The yearly output of wheat recorded for the last twenty five years, the weekly average price of eggs recorded for the last 52 weeks, the monthly average sales of a firm recorded for the last 48 months or the quarterly average profits recorded for the last 40 quarters etc., are examples of time series data. It may be observed that this data undergoes changes with the passage of time. A number of factors can be isolated which contribute to changes occurring over time in such a series.
In the fields of economics and business, data such as income, imports, exports, production, consumption, and prices depend on time. All of these data are dependent on seasonal changes as well as regular cyclical changes over the time period. To evaluate the changes in business and economics, the analysis of time series plays an important role in this regard. It is necessary to associate time with time series, because time is one basic variable in time series analysis.