Variance and Standard Deviation

Variance and Standard Deviation

Nomenclature

It is standard practice to use Greek letters to represent population parameters, and Roman letters to represent sample statistics.

Population Sample
 

Mean

μ

x

Variance σ2 s2
Standard Deviation σ s

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:

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