Two Outliers Can Make Your Data Look Perfectly Scattered
Range and standard deviation respond very differently to extreme values — range captures only the edges while standard deviation weighs every point. Drag the slider below to add outliers and watch how each measure reacts to the same dataset.
Dataset Viewer20 points clustered
Slider adds extreme outliers to the distribution
All points within 2 units of centre
NoneSomeMany
Range
4.0
Std Dev
0.6
Range is the simplest measure of spread — you just subtract the minimum value from the maximum value. While it's easy to calculate and understand, range has a critical weakness: it's completely determined by only two data points, the extremes. If a dataset has 1000 values tightly clustered around the mean but one outlier far away, the range will be huge even though 99.9% of the data shows minimal variation. This makes range useful for understanding the full extent of your data, but unreliable for describing typical spread when outliers are present.
Know This
Standard deviation measures the average distance of data points from the mean in the original units, making it the most informative measure of spread for symmetric distributions without extreme outliers.