7.7 Box Plots

A box plot is a schematic representation of the distribution of a variable. The left graph in Figure 7.11 shows a box plot for the US_Gross variable restricted to the G-rated movies in the Movies data set. (The left graph also shows the default appearance of a box plot in SAS/IML Studio.) The right graph shows a box plot for the same data, but labels important features of the box plot.

A box plot enables you to find the five-number summary of the data: the minimum value, the 25th percentile, the 50th percentile, the 75th percentile, and the maximum value. (The 25th, 50th, and 75th percentiles are also called the first quartile (Q1), the median, and the third quartile (Q3), respectively.) For example, Figure 7.11 indicates the five-number summary for the US gross revenues for G-rated movies. The minimum value is about 8 million dollars. The quartiles of the data are approximately 25, 55, and 85 million dollars. The maximum value is about 245 million dollars.