This chapter is from the book
This chapter is from the book
This chapter is from the book
2.3 “Bad” Charts
So-called “good” charts, such as the charts presented so far in this chapter, help visualize data in ways that aid understanding. However, in the modern world, you can easily find examples of “bad” charts that obscure or confuse the data. Such charts include elements or practices known to impede understanding or fail to apply properly the techniques that this chapter discusses.
Concept A “bad” chart fails to clearly present data in a useful and undistorted manner.
>Interpretation Using pictorial symbols obscures the data and can create a false impression in the mind of the reader, especially if the pictorial symbols are representations of three-dimensional objects. In Example 1, the wine glasses fail to reflect that the 1992 data (2.25 million gallons) is a bit more than twice the 1.04 million gallons for 1989. In addition, the spaces between the wine glasses falsely suggest equal-sized time periods and obscure the trend in wine exports. (Hint: Plot the data as a time-series chart to discover the actual trend.)
EXAMPLE 1: Australian Wine Exports to the United States.
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Example 2 combines the inaccuracy of using a picture (grape vine) with the error of having unlabeled and improperly scaled axes. A missing X axis prevents the reader from immediately seeing that the 1997–1998 value is misplaced. By the scale of the graph, that data point should be closer to the rest of the data. A missing Y axis prevents the reader from getting a better sense of the rate of change in land planted through the years. Other problems also exist. Can you spot at least one more? (Hint: Compare the 1949–1950 data to the 1969–1970 data.)
EXAMPLE 2: Amount of Land Planted with Grapes for the Wine Industry.
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When producing your own charts, use these guidelines:
Always choose the simplest chart that can present your data.
Always supply a title.
Always label every axis.
Avoid unnecessary decorations or illustrations around the borders or in the background.
Avoid the use of fancy pictorial symbols to represent data values.
Avoid 3D versions of bar and pie charts.
If the chart contains axes, always include a scale for each axis.
When charting non-negative values, the scale on the vertical axis should begin at zero.