Boxplots and 5-Number Summaries: Once we have a 5-number summary of a
(quantitative) variable, we can display that information in a boxplot.
1. Draw a single vertical axis spanning the extent of the data. Draw short
horizontal lines that are lower and upper quartiles and at the medium, then
connect them with vertical lines to form a box.
2. We erect “fences” around the main part of the data. We place the upper fence
1.5 IQRs above the upper quartile. We place the lower fence 1.5 IQRs below
the lower quartile.
The fences are just for construction and are not part of the display. We show
the, with dotted lines. Don’t include it in your boxplot.
3. We use the fences to grow “whiskers”. Draw lines from the ends of the box up
and down to the most extreme data values found within the fences. If a data
value falls outside one of the fences, we do not connect if with a whisker.
4. We display any data values lying beyond the fences with special symbols.
(We sometimes use a differe