<P> Rarely, box plots can be presented with no whiskers at all . </P> <P> Because of this variability, it is appropriate to describe the convention being used for the whiskers and outliers in the caption for the plot . </P> <P> The unusual percentiles 2%, 9%, 91%, 98% are sometimes used for whisker cross-hatches and whisker ends to show the seven - number summary . If the data is normally distributed, the locations of the seven marks on the box plot will be equally spaced . </P> <P> Since the mathematician John W. Tukey introduced this type of visual data display in 1969, several variations on the traditional box plot have been described . Two of the most common are variable width box plots and notched box plots (see Figure 4). </P>

When is a box and whisker plot used