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 Description  
 Box and Whisker Plot:  A diagram that summarizes data using the median, the upper and lower quartiles, and the extreme values (outliers).
In a box and whisker plot, a box is drawn around the quartile values, and the whiskers extend from each quartile to the extreme data points.

The box-and-whisker plot is good at showing the extreme values and the range of middle values of your data. The box shows us the middle values of a variable, while the whiskers stretch to the greatest and lowest value of that variable. The box-and-whisker plot was invented in the 1970's by John Tukey. In the 1960's John Tukey also invented the stem-and-leaf plot. This type of graph is useful when comparing one variable for several different groups. A box-and-whisker plot of that variable can be drawn for each group on one page, giving you a visual representation of the differences of that variable according to group. For example, the poverty rate of different countries might be compared by looking at the box-and-whisker for that country in relation to the box-and-whisker graph of the poverty rates of the other countries.

The box and whisker plot is sometimes called the five-number summary, because it uses five summary statistics for a certain variable. These summary statistics are:

Median - the middle of the data when it is arranged in order from least to greatest.

Lower quartile or 25th percentile - the median of the lower half of the data.

Upper quartile or 75th percentile - the median of the upper half of the data.

Minimum value - the smallest observation value.

Maximum value - the largest observation value.

 

    • the box portion of the box-and-whisker plot includes 50% of the data
    • the whiskers extend to the minimum and maximum data values
    • more than one box plot can be drawn for the number scale allowing comparison of a variable by groups
     


Example Box-and-Whisker Plots:

Quality Ratings of Natural Peanut Butters:



Comparing the Quality Ratings for Natural/Regular Peanut Butters:



Click here for instructions on creating a box-and-whisker plot.