Encoding Quantitative Data Inaccurately

Sometimes graphical representations of quantitative data are mistakenly designed in ways that display inaccurate values. In Figure 3-25, for instance, 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 in this graph 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: the revenue is actually less than double the costs. The problem is that the values begin at $500,000 rather than $0, as they always should in a bar graph.

Figure 3-25. This bar graph encodes the quantitative values as bars inaccurately, by failing to begin the scale at zero.