Among common measures of center, which is most robust to outliers?

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

Answer: (C)

When a value is extremely large or small, robustness to outliers means a statistic should not swing dramatically. The median fits this idea because it is the middle value after sorting the data, so its position depends on the order of observations, not their magnitudes. An outlier changes the extremes but often leaves the central position of the data unchanged, especially as the data set grows. For example, with values 1, 2, 3, 4, 100, the median is 3, while the mean jumps from 2.5 to 22 due to the outlier. The range, meanwhile, reflects only the extreme spread and is highly sensitive to outliers, and the mode focuses on frequency rather than a true center, making it less reliable as a measure of location in the presence of outliers. So the middle value after sorting is the most resistant to the influence of extreme observations.