Which measure of center is most robust to outliers?

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

Answer: (C)

When data include extreme values, the measure of center that stays reliable is the median. The median depends on the order of the data and the middle position, so the actual sizes of any outliers don’t pull it toward extreme values. In contrast, the mean uses every data value, so a very large or very small outlier shifts it toward that value, making it less robust to outliers.

For example, with a data set like 1, 2, 3, 4, 1000, the median is around 3.5 (the middle of 3 and 4), while the mean becomes heavily influenced by the 1000, giving a very large number. The range measures spread, not center, and the mode reflects the most frequent value—both of these are not reliable center measures in the presence of outliers, or may not even exist in some data sets.