Which statistics are easily affected by outliers?

• A. Mean and Range
• B. Median and Mode
• C. Standard Deviation and Median
• D. Range and Mode

Answer: (A)

Outliers have the biggest impact on measures that rely on every value or on the extremes of the data. The mean averages all data points, so an extremely large or small value pulls that average toward itself. The range is simply the difference between the largest and smallest values, so an outlier at either end directly widens the range. Because of that, mean and range are the statistics that are most easily distorted by outliers.

In contrast, the median is the middle value when the data are ordered, so a single outlier doesn’t move it much. The mode is just the most frequent value, and a rare extreme value won’t typically become the most common. For illustration, with data like 1, 2, 3, 4, 1000, the mean jumps to about 202, the median stays at 3, and the range becomes 999, showing how the mean and range react strongly to the outlier while the median and mode do not.