Which measure of a data set is least affected by outliers?

• A. Mean
• B. Mode
• C. Range
• D. Median

Answer: (D)

Outliers don’t change where the center sits when you’re using the median. The median is the middle value when the data are ordered, so extreme values at one end barely budge its position. In contrast, the mean adds up all values, so a single very large or very small number pulls the average toward it, and the range depends on the smallest and largest values, so an outlier can dramatically widen it. A quick example helps: with 1, 2, 3, 4, and 100, the median is 3, the mean is 22, and the range is 99. That shows why the median stays most resistant to outliers.