Statistics

Ignoring How Outliers Affect the Mean

Students treat the mean as a typical value even when one outlier pulls it far away from most of the data.

Quick check

Why students make it

Students often think the mean always describes the center of a data set. They forget that every value is included in the sum, so one very large or very small value can move the mean a lot.

The rule done right

The mean is sum of valuesnumber of values\frac{\text{sum of values}}{\text{number of values}}, so outliers affect it. When a data set has an outlier, compare the mean with the median before saying what is typical.

Related resources

meanoutliersmedian