Standard Deviation
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The standard deviation is a popular measure of variability. The standard deviation is the square root of the variance.
Population Standard Deviation
The population deviation is denoted by 
. It is given by the formula:
The capital Greek letter sigma 
is commonly used in mathematics to represent a summation of all the numbers in a grouping.
N is the number of terms in the population.
Sample Standard Deviation
The sample standard deviation is denoted by s. It is given by the formula
Like the variance, the standard deviation utilizes the sum of the squared deviations about the mean. It is computed by averaging these squared deviations and taking the square root of that average. One feature of the standard deviation that distinguishes it from a variance is that the standard deviation is expressed in the same unit as the raw data, whereas, the variance is expressed in those units squared.
The following video will give:A review of Population Mean and Sample Mean, Population Variance and the Sample Variance.
An introduction to Population Standard Deviation and Sample Standard Deviation.
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