Microsoft Office Tutorials and References
In Depth Information
Adding a trendline
Trendlines assume that the category axis contains equal-interval values. This
will always be the case with XY charts, bubble charts, and other chart types that
use a time-based category axis. For example, a line chart that displays months or
weeks along its category axis is a candidate for a trendline — as long as there are no
gaps in the data.
Charts that use an arbitrary category axis are not appropriate for a trendline,
although Excel won’t object if you add one. If the chart uses an arbitrary category
axis, the trendline interprets the categories as values beginning with 1 and
incrementing by 1.
Figure 5-2 shows a column chart with a trendline. Because the category axis
contains non-numeric text, Excel assigned the value of 1 to Ruth, 2 to Jerry, 3 to
Pam, and so on. Consequently, the trendline is completely meaningless.
Figure 5-2: This chart is not appropriate for a trendline.
Figure 5-3 shows an example of a chart that is appropriate for a trendline. In this
case, the chart compares individual performance on two tests using an XY chart.
Because both axes are numeric, the trendline is valid. It indicates a positive linear
relationship: Students who did well on Test 1 also tended to do well on Test 2.
Adding a trendline
A trendline is always associated with a particular data series. Although you might
expect this option to appear in the Format Data Series dialog box, it doesn’t. To add
a trendline to a chart series, select the series and then choose Chart
Add Trendline
to display the Add Trendline dialog box (see Figure 5-4). Or, you can right-click a
data series and choose Add Trendline from the shortcut menu.
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