Standard deviation

The standard deviation (denoted by the Greek letter σ) gives the degree of variation around the mean value of a stochastic variable. It is calculated as follows:

σ² = ∑ (x_i - <x>)² / (n-1)

where x_i (i = 1, 2 ... , n) is the result of an individual observation, <x> is the mean value and n is the number of observations.

Related concepts

• error propagation
• mean value
• statistics
• stochastic variable