How it is calculated
Mean x̄ = Σx ÷ n Sample variance s² = Σ(x − x̄)² ÷ (n − 1) Population σ² = Σ(x − x̄)² ÷ n Standard deviation = √varianceThe median is the middle value after sorting (or the mean of the two middle values); the mode is the most frequent.
Worked example
Data 4, 8, 6, 5, 3, 8, 9: mean = 43 ÷ 7 ≈ 6.14, median 6, mode 8, sample standard deviation ≈ 2.27.
Frequently asked questions
Sample or population?
Use the sample formula (n − 1) if your data is part of a larger group; population if it is all of it.
When is the median better than the mean?
With outliers, like salaries, since the median is not affected by them.
What does standard deviation mean?
How spread out the data is around the mean; larger means more spread.