The standard deviation is a commonly used measure of spread of a data set. It is a measure of how much the data elements differ from the mean. To denote the standard deviation, the Greek letter σ is commonly used, which is read as sigma.
The standard deviation is the quadratic mean of the difference between the data values xi and the mean xˉ.
σ=n(x1−xˉ)2+(x2−xˉ)2+…+(xn−xˉ)2
The applet below calculates the standard deviation for the data set on the number line.
Move the points around to change the data.