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Standard Deviation and Variance

Asked May 11, 2007, 06:46 PM — 11 Answers
How do you figure standard deviation and variance when you have a group or list of numbers.

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11 Answers
gogosean's Avatar
gogosean Posts: 47, Reputation: 37
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#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.


Let me know what kind of help you need.
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NeedKarma's Avatar
NeedKarma Posts: 10,230, Reputation: 8855
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#3

May 11, 2007, 07:29 PM
Here is a good explanation: Learn Standard Deviation tutorial, definition, example, formula
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gogosean's Avatar
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.
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pawar_bb's Avatar
pawar_bb Posts: 5, Reputation: 1
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#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
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csl8back's Avatar
csl8back Posts: 1, Reputation: 1
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#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.
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statsman's Avatar
statsman Posts: 1, Reputation: 1
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#7

Dec 4, 2008, 06:00 PM
This page might help with calculating standard deviation:

Standard Deviation Example
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sixsigmais's Avatar
sixsigmais Posts: 6, Reputation: 1
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#8

Aug 24, 2009, 03:19 AM
Use excel formula
=STDEV( numbers)
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u069188's Avatar
u069188 Posts: 2, Reputation: 1
New Member
  
#9

Feb 10, 2010, 02:20 PM
Quote:
Originally Posted by gogosean View Post
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!
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sveegaard's Avatar
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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