What Is Variance in Statistics?
Variance is the average of the squared differences between each value and the mean of a data set. It measures how far values spread from the mean. Because the differences are squared, variance is expressed in squared units; its square root is the standard deviation.
Formula
Population variance σ² = Σ(x − mean)² ÷ n. Sample variance s² = Σ(x − mean)² ÷ (n − 1).
Variance vs. Standard Deviation
Both measure spread. Standard deviation is easier to interpret because it uses the same units as the data, while variance is convenient in many statistical formulas.
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Last updated: September 27, 2026. This definition is for general educational purposes only. It is not financial, investment, tax, legal, or medical advice, and it does not recommend any product or course of action. For decisions about your own situation, consult a qualified professional.