A box plot shows the five-number summary of the data – the minimum, first quartile, median, third quartile, and maximum. An outlier box plot is a variation of the skeletal box plot that also identifies possible outliers.
Skeletal box plot
A skeletal box plot shows the median as a line, a box from the 1st to 3rd quartiles, and
whiskers with end caps extending to the minimum and maximum. Optional notches in the box
represent the confidence interval around the median.
Outlier box plot
An outlier box plot is a variation of the skeletal box plot, but instead of extending to the minimum and maximum, the whiskers extend to the furthest observation within 1.5 x IQR from the quartiles. Possible near outliers (orange plus symbol) are identified as observations further than 1.5 x IQR from the quartiles, and possible far outliers (red asterisk symbol) as observations further than 3.0 x IQR from the quartiles. You should investigate each possible outlier before deciding whether to
exclude it, as even in normally distributed data, an outlier box plot identifies approximately 0.7% of observations as possible outliers.
Quantile box plot
A quantile box plot is a variation on the skeletal box plot and shows the whiskers extending to
specific quantiles rather than the minimum and maximum value.