A standard deviation, in its' simplest definition, is nothing more than a mean of the mean. It defines how closely all the numbers are gathered towards the mean. To get the standard deviation, you will first need to calculate the mean. You will also need to make a table where you will subtract the mean from each of the variables. You can find more information here: http://www.ltcconline.net/greenl/courses/201/descstat/mean.htm
