Standard deviation is used to measure the amount of variation of a set of values. A low standard deviation indicates that the values tend to be close to the mean of the set, while a high standard deviation indicates that the values are spread out over a wider range.
There are 2 types of equations: Sample and Population.
Population Standard Deviation
Population Standard Deviation (σ) is used with an entire population or with sample of a large population which could be genealized to a population.
µ: Population average
Xi: Individual values
N: Count of values
Sample Standard Deviation
Sample Standard Deviation (s), is used to make a statement about the population standard deviation from wich sample is drawn.
x¯: Sample average
Xi: Individual values
N: Count of values