# Standard Deviation and Variance

How do you figure standard deviation and variance when you have a group or list of numbers.

 gogosean Posts: 47, Reputation: 37 Junior Member #2 May 11, 2007, 07:26 PM
Quote:
 Originally Posted by garrett7115 How do you figure standard deviation and variance when you have a group or list of numbers.
Do you need to show how you have done it by hand, or do you want an Excel solution?

The good news is, if you have to do it by hand, the Standard Deviation is simply the square root of the variance.

 NeedKarma Posts: 10,230, Reputation: 8855 Uber Member #3 May 11, 2007, 07:29 PM
Here is a good explanation: Learn Standard Deviation tutorial, definition, example, formula
 gogosean Posts: 47, Reputation: 37 Junior Member #4 May 11, 2007, 07:32 PM
If you need the notation explained, just let me know. Some people need a process map instead of a formula.
 pawar_bb Posts: 5, Reputation: 1 New Member #5 Jul 12, 2007, 09:11 PM
In excel you can use function standard deviation and get answer in few seconds
Variance is square of std deviation
 csl8back Posts: 1, Reputation: 1 New Member #6 Jul 17, 2007, 07:16 PM
Quote:
 Originally Posted by garrett7115 How do you figure standard deviation and variance when you have a group or list of numbers.
 statsman Posts: 1, Reputation: 1 New Member #7 Dec 4, 2008, 06:00 PM

Standard Deviation Example
 sixsigmais Posts: 6, Reputation: 1 New Member #8 Aug 24, 2009, 03:19 AM
Use excel formula
=STDEV( numbers)
 u069188 Posts: 2, Reputation: 1 New Member #9 Feb 10, 2010, 02:20 PM
Quote:
 Originally Posted by gogosean Do you need to show how you have done it by hand, or do you want an Excel solution? The good news is, if you have to do it by hand, the Standard Deviation is simply the square root of the variance. Let me know what kind of help you need.
I would like both an excel solution and a process map, if you please!
 sveegaard Posts: 13, Reputation: 10 New Member #10 Feb 21, 2010, 10:29 AM
Excel (if your numbers are in cell A1 to A20): =stdev(A1:A20)

"By hand":
1) Find the mean (I will call this X)
2) For every number (Xi), calculate (Xi - X)^2 (that is, the difference between the number and the mean, squared. I will call this Z^2)
3) Sum up all Z^2 (I will call this Sum(Z^2))
4) Divide Sum(Z^2) with the number of numbers minus one (that is, if you have 50 numbers, divide by 49).
5) Take the squareroot of the value you get in step 4.

This is for what is called experimental standard deviation.

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