Visualising quantitative data (Boxplot)
(or box-and-whiskers plot) is a graphical representation of
the five-number summary.
Because the whiskers must end at an observed data point, the whisker
lengths can look unequal, even though 1.5 IQR is the same for both sides.
Observed data points outside the boundary of the whiskers are plotted as
outliers and are flagged as unusual.
Probability Models and Data Analysis (STAT2203/7203 Semester 2, 2022) - Lecture 1.3