To find the standard deviation for a set of data, use the following steps:
1. Use a table or spreadsheet and list your data in the first column. The data does not need to be in order, but it is a good habit to do this.
2. Find the mean for your set of data.
3. In the second column, find the difference between each observation and the mean. You may either go observation minus mean or mean minus observation. You need to use the same method throughout though. The sum of this column will be 0. If not, go back and find your error.
4. In the third column, you will square each of the differences in the second column. Remember when you square a value it always becomes positive.
5. Find the sum of the third column and divide by the number of values you have in your set. This is your VARIANCE.
6. To get your STANDARD DEVIATION, take the square root of your variance.