Suppose you wanted to compare the performance of three lathes responsible for the rough turning of a motor shaft. Right figure: For comparison, a histogram of the data is also shown, showing the frequency of each value in the data set. The median value is displayed inside the "box." The maximum and minimum values are displayed with vertical lines ("whiskers") connecting the points to the center box. Left figure: The center represents the middle 50%, or 50th percentile of the data set, and is derived using the lower and upper quartile values. The data represented in box and whisker plot format can be seen in Figure 1. Note: For a data set with an even number of values, the median is calculated as the average of the two middle values. Maximum value: The largest value in the data setįor example, given the following 20 data points, the five required statistics are displayed.Third quartile: The value above which the upper 25% of the data are contained.Median value: The middle number in a range of numbers.Second quartile: The value below which the lower 25% of the data are contained.
Why Use a Box and Whisker Plot?īox and whisker plots are very effective and easy to read, as they can summarize dataįrom multiple sources and display the results in a single graph. Plot can provide additional detail while allowing multiple sets of data to be displayed in the same graph. In most cases, a histogram analysis provides a sufficient display, but a box and whisker Quality Glossary Definition: Box and whisker plotĪlso called: box plot, box and whisker diagram, box and whisker plot with outliersĪ box and whisker plot is defined as a graphical method of displaying variation in a set of data.
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