Pub. date: 2008 | Online Pub. Date: November 27, 2007 | DOI: 10.4135/9781412953948 | Print ISBN: 9781412928168 | Online ISBN: 9781412953948| Publisher:SAGE Publications, Inc.About this encyclopedia
The box-and-whisker plot, also called a boxplot, was invented by John Tukey. It is a graph of a data set that consists of a line extending from the minimum value to the maximum value, and a box with lines drawn at the first quartile Q 1 ; the median, the second quartile; and the third quartile Q 3 , with outliers plotted as individual data points. It is useful for revealing the central tendency and variability of a data set, the distribution (particularly symmetry or skewness) of the data, and the presence of outliers. It is also a powerful graphical technique for comparing samples from two or more different treatments or populations. Although boxplots are usually generated using statistical software, they also may be constructed by hand, using the following steps: 1. Draw a rectangular box whose left edge 1 ...