Variance and Standard Deviation
It is standard practice to use Greek letters to represent population parameters, and Roman letters to represent sample statistics.
The formula for calculating the mean of a population is:
The formula for calculating the variance and standard deviation of a population is:
The formula for calculating the mean of a sample is:
The formula for calculating the variance (S2) and standard deviation (S) of a sample is:
However when making inferences about a population from a sample, then the following formulas are used for the variance and the standard deviation: