Special Edition Using Microsoft Office PowerPoint 2003

A trendline creates a forecast of future trends based on existing data. For example, you can use a trendline to predict future revenues based on existing revenue data in a chart. This is also referred to as regression analysis .

You can use trendlines to make basic forecasts, but a solid understanding of regression analysis and statistics is necessary to make the best use of this feature.

You can display a trendline in unstacked area, bar, column, line, stock, XY (scatter), and bubble charts that don't have a 3D effect.

To create a trendline, follow these steps:

1. Choose Chart, Add Trendline to open the Add Trendline dialog box, shown in Figure 11.27.

   Figure 11.27. Predict future values by creating a trendline.

   Can't access the Add Trendline menu option ? See the " Troubleshooting " section near the end of this chapter.

2. Choose the Trend/Regression Type, such as Linear or Moving Average, from the group box.

3. Select the data series on which you want to base the trend from the Based on Series list.

4. Click the Options tab for more options, shown in Figure 11.28.

   Figure 11.28. Specify the period of time you want to forecast.

5. You can enter a custom name for the trendline or accept the default. The default uses the type of trendline you selected in the Type tab, followed by the series name in parentheses.

6. Indicate how many periods you want to forecast either forward or backward. For example, if your chart displays data for four quarters and you choose to forecast four periods forward, PowerPoint displays trends for the next full year in quarterly increments .

7. Click OK to apply the trendline.

Figure 11.29 shows a sample trendline. Based on actual data from the past year, it forecasts for the next year how long callers to a help line will have to wait on hold before speaking to someone.