A variety of graphic
displays can be used to give an effective visual summary
of key descriptive statistics
for a data set. One of these is a box plot
, which is also called a box-and-whisker plot
A box plot shows the smallest and largest values of a data set
, the first and third quartile
s and the median
. By presenting these key descriptive statitsics, the box plot also shows the range
Minimum Median Maximum
| | |
| First | Third |
| quartile | quartile |
| | | | |
| \|/ \|/ \|/ |
| ___________________ |
\|/ | | | \|/
._______| | |_______________________.
| | |
The above diagram shows a prototype box plot (as best depicted within a HTML
environment). The plot has been displayed horizontally but it could also be displayed vertically.
The extremeties of the plot (the ends of the whiskers) correspond to the smallest and largest observations in the data set, the distance between these represents the range.
The ends of the box are positioned at the first and third quartiles of the data set, hence the length of the box represents the interquartile range.
The partitioning line within the box is drawn at the median of the data set.