In this example, the first quartile is 47.5 and the third quartile is 62. It is not really surprising when you consider that we are doing a 5 number summary on a set of only 9 numbers. Drawing the Whiskers The commonly accepted method among statisticians for drawing the whiskers is somewhat more complicated than that described in most senior secondary texts written to the Queensland syllabuses. To draw the whisker above the 3 rd quartile, draw it to the largest data value that is less than or equal to the value that is 1.5 IQRs above the 3 rd quartile. Any data value larger than that should be marked as an outlier.
Some statisticians differentiate between 'mild' outliers and 'severe' outliers.
Mild outliers lie between 1.5 and 3 IQRs above the 3 rd quartile while severe outliers are more than 3 IQRs above the 3 rd quartile. I don't believe we need to make the distinction between mild and severe outliers in our courses. The IQR is 6. Now 1.5 times 6 equals 9. This is the maximum length of the whisker.