Renáta Németh, Dávid Simon
A graphic device that presents the range, the IQR, the median, the maximum and the minimum values within one figure.
A box is drawn between the lower and upper quartiles,
a solid line presents the median within the box,
the maximum and minimum values are presented by a vertical line outside the box (called whiskers, therefore frequently called box-and-whiskers-plot)
It gives us a quick visual impression of the spread in the distribution and of the shape of the distribution.
Compare the figures below!
Detecting differences in central tendency using a box plot
Detecting differences in variability using a box plot
Detecting skewness using a box plot
Detecting outliers using a box plot
Box plots have many different definitions. E.g. SPSS draws box plots which show the median and the IQR, but instead of the range, they present two types of extreme values (called outliers and extremes).