What is Standard Deviation?

The standard deviation is a popular measure of variability. It is used both as a separate entity and as a part of other analyses, such as computing confidence intervals and in hypothesis testing. The standard deviation is the square root of the variance. The population standard devia­tion is denoted by σ. Like the variance, the standard deviation utilizes the sum of the squared deviations about the mean (SSx). It is computed by averaging these squared deviations (SSX/N) and taking the square root of that average.