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-numbersummary,
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.