For example , consider a population consisting of the following eight values : These eight data points have the mean ( average ) of 5 : First , calculate the difference of each data point from the mean , and square the result of each : Next , calculate the mean of these values , and take the square root : This quantity is the population standard deviation , and is equal to the square root of the variance .
Consider a group having the following eight numbers : These eight numbers have the average ( mean ) of 5 : To calculate the population standard deviation , first find the difference of each number in the list from the mean .