The statistical data 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 quarter etc., are example 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 with contribute to the changes occurring overtime in such series.
In the field of economics and business, for example, income, imports exports, production, consumption, prices these data are depend on time. And all of these data are pretentious by 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 associated time with time series because time is one basic variable in time series analysis.