Using a pocket calculator to compute a standard deviation

Steve Simon

2007-03-01

Categories: Blog post Tags: Descriptive statistics

the time

Your pocket calculator must have a square root key. A memory key (M+) is helpful. Here’s a picture of a nice pocket calculator with both features from www.keysan.com.

Suppose you wanted to calculate the standard deviation of the following four numbers: 12

First you need to clear out memory. For some calculators

Now enter each data value in succession and press the M+ button.

12 M+ 10 M+ 11 M+ 13 M+

Press the recall memory button to get 46 and clear memory. Square this number to get 2116 and divide by the sample size (in this case, 4) to get 529. Write this number down. Now enter each data value again

12 X M+ 10 X M+ 11 X M+ 13 X M+

will suffice because the calculator will finish the squaring operation before adding to memory. For other calculators

12 X = M+ 10 X = M+ 11 X = M+ 13 X = M+

Press the recall memory button to get 534. Subtract the number you wrote down earlier to get 5. Divide by n-1 (in this case

As a quick double check of the accuracy of your calculations compute the range of the data (largest value minus the smallest value). The range is usually 4 to 6 times larger than the standard deviation . In this example the range is 3

Repetition is the best teacher

Try to calculate the standard deviation of the following data: `2.1

You should get 1.57734 for the standard deviation. If you didn’t get this value

On your own