Standard deviation is a number used to tell how measurements for a group are spread out from the mean value. In other words, it's a measure of how spread out the data is.
Its symbol is "σ". Also, we can call it "Sigma"(The greek alphabet).
The following formulas are used to calculate the standard deviation.
Population Standard Deviation Formula:
Sample Standard Deviation Formula:
There is a small but very important difference between population and sample standard deviation formula. That is "N" and "N-1" at denominator. Therefore, when we calculate for sample standard deviation, we need to divide by "N-1" (Instead of "N").
Here N is for population size and N-1 is for sample size. Whereas other components are same in both equations.
Also, "μ" and "x̄" (x-bar) are the same things. That is mean. x̄ is the sample mean and μ is the population mean.