EXAMPLE 5 A misleading graph

Figure 10.6 is a pictogram. It is a bar graph in which pictures replace the bars. The graph is aimed at consumers shopping for a vacuum. It claims that a Dyson vacuum has more than twice the suction of any other vacuum. The numbers above the vacuums show the calculated air watts for three vacuums. We see the Dyson vacuum (far right) has roughly four times the air watts (160 is roughly 4 times 43) of the vacuum on the far left. However, this graphic makes it appear as though there is a much larger difference. Why is this?

To magnify a picture, the artist must increase both height and width to avoid distortion of the image. By increasing both the height and width of the Dyson vacuum, it appears to be 4 × 4 = 16 times larger. Remember a bar graph should have bars of equal width—only the heights of the bars should vary. Replacing the bars on a bar graph with pictures is tempting, but it is difficult to keep the “bar” width equal without distorting the picture.