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Excel 2003: The Missing Manual by Matthew MacDonald

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Improving Your Charts

So far, you've learned the key techniques you need to make sure your charts tell the right story. However, Excel lets you do plenty more, including adding trendlines, data tables, and error bars, and tweaking 3-D perspective and shapes. In the following sections, you'll learn even more about how to make the perfect chart.

Adding a Trendline

One of the main reasons that people create charts is to reveal patterns that are hidden in the data. For example, a gift card company might look at a historical record of sales to make an educated guess about the upcoming holiday season. Or, a researcher might look at a set of scientific data to find out if potatoes really can cure the common cold. In both these examples, what's most important is spotting the trends that lurk inside most data collections.

One of the easiest ways to spot a trend is to add a trendline to your chart. A trendline is similar to an ordinary line in a line chart that connects all the data points in a series. The difference is that a trendline assumes the data isn't distributed in a perfectly uniform pattern. Instead of exactly connecting every point in a series, a trendline shows a line that best represents all the data on the graph, which means that minor exceptions, experimental error, and ordinary variances don't distract Excel from finding the overall pattern. Figure 17-11 shows an example.

This example shows the comparison between age and reaction time that was introduced in the last chapter. The difference here is that the trendline has been extended beyond the actual data to predict results for people who are younger than 40.

Figure 17-11. This ...

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