Standard Deviation
A statistical measure of the spread of a set of repeated measurements about their mean.
Formula / equation
s = √(Σ(xᵢ − x̄)² / (n − 1))
Unit
Various
In depth
The sample standard deviation uses n − 1 in the denominator to correct for the fact that the mean was itself estimated from the data. Dividing it by the mean gives the relative standard deviation, which allows precision to be compared across different measurement scales.
Examples in the real world
Titres of 24.55, 24.57 and 24.56 mL giving a standard deviation of 0.01 mL.