Graphical plots and figures can be extremely powerful tools for understanding data and representing analysis results. The famous Anscombe’s Quartet, shown below, is a classic example of the value of data visualization. These four data sets have identical summary statistics—the mean values, variances, and best-fit regression lines are all the same—but plotting the underlying data shows them to have very different distributions.




However, data visualization tools must be used with caution. Inappropriate use of colors, scales, labels, and data selection can easily lead to misinterpretation. The figure below has expenses and revenues plotted on two separate vertical scales in a sneaky attempt to show that expenses (red line) are increasing at a faster rate than revenues (blue line). 




Representing the two values by their relative changes over the indicated time period shows that revenue has increased nearly 2.5 times as quickly as expenses.