Identifying outliers

In box plots, an outlier can be identified when using technology. This function may be turned on or off.

In the Australian Curriculum: Mathematics, an outlier is described as any data point that is more than 1.5 times the interquartile range (IQR, where IQR = Q3 – Q1) from either the upper quartile (Q3) or the lower quartile (Q1).


Box plot, outlier shown on the left with a circle, no connecting whisker.

Produced with outlier function 'on'.

Box plot, extreme value included on left, with connecting whisker.

Produced with outlier function 'off'.


In the box plot above, any value less than 8.5 is an outlier.

Q1 – (1.5 \(\times\) IQR)= 13 – (1.5 \(\times\) 3) = 8.5

The Beware of Outliers: Student Worksheet provides an activity based on outliers and the mean. You can also download the Beware of Outliers: Teacher Notes.

Curriculum links

Year 8: Investigate the effect of individual data values, including outliers, on the mean and median