All of these distributions have the same mean (62%) but you can see that they differ greatly. The difference lies in their spread. Set A is the most spread out, while C is the most clustered. One way of quantifying this spread is with the standard deviation, which is denoted with s.
To calculate the standard deviation, first find (x - ) for each point, square the results, add them, divide by n-1, and finally take the square root. The formula is:
For computerized calculations and for estimating the cumulative standard deviation, the equation that is frequently used is: