Most textbooks in elementary statistics will ask you to find the standard deviation in the binomial probability distribution chapter. This can be a challenge, because the variance and standard deviation formulas are daunting when you first look at them. This how to will tell you how to find a standard deviation for a binomial distribution in just a few steps.
- Step 1: Find the mean. If you don’t know how, see how to find the mean using a probability distribution.
- Step 2: Square the mean from step 1. For example, if your mean is .9, .9²=.81. Set this number aside.
Step 3: Make a probability distribution chart.
- Step 4: Square the top number (X) in each column and multiply it by the bottom number in the column (P(X)). For example 0²*0.09 from the first column, 1²*0.07. Repeat for all columns.
- Step 5: Add all of the numbers in step 4 together.
- Step 6: Subtract the number you found in step 2 from the number you found in step 5.
Step 5-Step 2=?.
- Step 6: Take the square root of the number you found in step 6.