In
descriptive statistics, a
box plot or
boxplot is a convenient way of graphically depicting groups of numerical data through their
quartiles. Box plots may also have lines extending vertically from the boxes (
whiskers) indicating variability outside the upper and lower quartiles, hence the terms
box-and-whisker plot and
box-and-whisker diagram.
Outliers may be plotted as individual points. Box plots are
non-parametric: they display variation in samples of a
statistical population without making any assumptions of the underlying
statistical distribution. The spacings between the different parts of the box indicate the degree of
dispersion (spread) and
skewness in the data, and show
outliers. In addition to the points themselves, they allow one to visually estimate various
L-estimators, notably the
interquartile range,
midhinge,
range,
mid-range, and
trimean. Boxplots can be drawn either horizontally or vertically.