Box plot

In descriptive statistics, a box plot is a convenient way of graphically depicting the five number summary, which consists of the smallest observation, lower quartile, median, upper quartile and largest observation.

The box plot may also identify outliers and possibly the mean.

A plain-text version might look like this:

                            +-----+-+
  *           o     --------|   + | |----
                            +-----+-+

+---+---+---+---+---+---+---+---+---+---+
0   1   2   3   4   5   6   7   8   9  10

For this data set (values are approximate, based on the figure):

• smallest observation (minimum) = .5
• lower quartile = 7
• median = 8.5
• upper quartile = 9
• largest observation (maximum) = 10
• mean = 8
• the value 3.5 is a "mild" outlier
• the value .5 is an "extreme" outlier
• the smallest value that is not an outlier is 5
• the data is skewed to the left (negatively skewed)