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© 2005 Perceptual Edge
PITFALL #8: ENCODING QUANTITATIVE DATA INACCURATELY
When you use a graph to communicate quantitative data, the values are encoded in the form of visual objects, such as the
bars on the graph below. These visual objects should accurately encode the values so you can compare them to one another
as a means to compare the values and understand the relationships.
Sometimes graphical representations of quantitative data are actually mis-designed in ways that inaccurately display the
quantities. The quantitative scale along the vertical axis was improperly set for a graph that encodes data in the form of bars.
The length of a bar represents its quantitative value. The bars that represent revenue and costs for the month of January
suggest that revenue was about four times costs. An examination of the scale, however, reveals the error of this natural
assumption: revenue is actually less than double the costs.
Figure 10: This graph, taken from a dashboard, illustrates
several problems in design that hinder communication.
Figure 11: The heights of the bars in this graph do not
accurately encode the values they represent.
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