Investigate the effect of individual data values , including outliers, on the mean and median (ACMSP207)

LO: To identify the effects of an outlier on data.


  • What an outlier is
  • How to calculate the mean of a set of data
  • How to calculate the median of a set of data
  • How to calculate the mode of a set of data
  • How to calculate the range of a set of data


  • That outliers can sometimes cause issues to the interpretation of collected data and that the removal of outliers helps us to get a more accurate representation of data.


  • I can identify the effect of outliers to a set of collected data.


Outliers is data which don’t fit the general trend. They tend to be away from where the majority of the data lies.

Effect of Outliers on Data

Outliers can skew data especially the mean and median from a data set.

If you look at the effects below, without outliers the mean of the data set was 3. If you have outlying data with a value of 10, it changed the mean to 4. In this case the mean didn’t shift that much.

But if you look in the second scenario, you have the same data set but with 300 as an outlier. The mean shifted from 5.45 to 30, which is a huge shift.

So 1 outlying value can have significant changes to the mean (average) of a data set.

Outlier Videos

Practise Questions

Year 8 Big Ideas 9C

Pg. 323 Explore: Q. 8a

Year 8 Big Ideas 9F

Pg. 334 Explore: Q. 7

My Maths 8

Exercise 9C pg. 475 Q. 11

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