Outliers - GCSE Maths Definition

In GCSE Mathematics, an outlier is a value in a data that does not follow the general pattern of the majority of the data. It may be a particularly high value compared to the others, or a particularly low value. A data set may have more than one outlier. An example would be to look at the cost of new cars - most will be in the tens-of-thousands of pounds, but the odd one or two may be particularly expensive, such as a rare sports car, that cost hundreds-of-thousands of pounds.

It is important to recognise outliers, and consider their effect on the data set. High outliers will increase the mean average; low outliers will decrease it. In larger data sets, the median will be unaffected by outliers. Outliers can be genuine data values (as in the case of the sports car), they could be due to one-off unusual events (a drought leading to low rainfall), or, could be a misreading/recording when the data was collected. It may be that we cannot tell from the information given.