Box-and-Whisker Plots: The Basics
What are the parts of a box-and-whisker plot?
When is it appropriate to use a box plot?
What are box-and-whisker plots?
A box-and-whisker plot, or simply a box plot, is a graphical representation of the range and distribution of numerical data (continuous or noncontinuous). This way of organizing data was invented in
1977 by John Tukey.
Here is an example of a box-and-whisker plot.
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What are the parts of a box-and-whisker plot?
A box plot summarizes data using the median, the upper and lower quartiles, and the upper and lower extremes.
The lowest value in the data set is called the lower extreme; the highest number is called the upper extreme. The middle value in the whole data set is the median. The number half-way between the lower extreme and median is the lower quartile, or 25th percentile, and the number half-way between the median and the upper extreme is called the upper quartile, or 75th percentile.
Each of these values is plotted on a number scale.
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When is it appropriate to use a box plot?
A box-and-whisker plot is useful for comparing one variable within a group.
Here are some examples of situations in which data can be appropriately displayed in box-and-whisker plots. Can you think of any more?
- Test scores for a single class and test
- Number of cars a salesman sold each month
- Average daily temperature in Detroit during a one-month span
- Ages of female althletes on the U.S. Olympic team
- Touchdowns made in one season by a professional football team
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