Sample vs population
Use population standard deviation when the dataset contains every value in the group you care about. Use sample standard deviation when the dataset is a sample used to estimate a wider population.
Example
For the dataset 2, 4, 4, 4, 5, 5, 7, 9, the mean is 5. Population standard deviation is 2 because the values are typically about 2 units away from the mean.
Common mistakes
Choose sample when your numbers are a subset of a wider group, and population only when the dataset contains every value you intend to describe. Also check outliers before relying on the standard deviation alone.
Formula
Population variance divides squared deviations by n. Sample variance divides by n - 1. Standard deviation is the square root of variance.
How to read the summary
The page also shows quartiles, median and IQR alongside mean, variance and standard deviation. These nearby statistics help you spot skew, outliers or data-entry mistakes before relying on the standard deviation alone.
References
- Khan Academy: Sample and population standard deviation, accessed 2026-05-14.
Last reviewed: 2026-05-14