Time series data
Many data sets contain measurements that are made sequentially at regular intervals. These data are called time series.
Time series data are widely analysed in the business world — accurate forecasting of exchange rates, share prices, demand for products and other business variables can have a major effect on profitability.
The importance of plotting
It is often difficult to get useful information from time series if they are presented in tabular form. As with other data structures, the information in a time series is most easily understood from a graphical display.
A time series plot is a type of dot plot in which the values are displayed as crosses against a vertical axis. The horizontal axis spreads out the crosses in time order. (It can also be thought of as a scatterplot in which the 'explanatory' variable is time.) The successive crosses are often joined by lines.
Defence Investment in USA
The table below describes the percentage of American Gross Domestic Product that was invested in defence between 1947 and 2013.
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Although it is possible to see some patterns in this table, the trends are clearer in a time series plot.
Click on points to read off exact expenditures.
Use the checkbox Join crosses to join successive crosses. This makes the movement of the series over time stand out better.
It is interesting to try to associate the peaks and dips in this time series plot with government administrations and international events! A manufacturer in the defence sector might also hope to predict future government expenditure from the trend in recent years.