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Standard Deviation

 
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lovelasagne
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Joined: 04 Feb 2009
Posts: 1

PostPosted: Wed Feb 04, 2009 6:17 pm    Post subject: Standard Deviation Reply with quote

I'm not great at maths and trying to work out standard deviation for some numbers. All the example calculations I find are very hard to follow. Could someone give a link to an easy example if he/she knows one.
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Theodore
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Joined: 06 Oct 2005
Posts: 2122
Location: Missouri, US

PostPosted: Fri Feb 06, 2009 7:34 pm    Post subject: Reply with quote

I'm going to use the example numbers 12, 3, 10, and 7.

1) Find the average of your numbers:

(12 + 3 + 10 + 7) / 4 = 32 / 4 = 8

2) Find the distance of each number from the average:

12 - 8 = 4, 3 - 8 = -5, 10 - 8 = 2, 7 - 8 = -1

3) Square each of these distances:

4 * 4 = 16, -5 * -5 = 25, 2 * 2 = 4, -1 * -1 = 1

4) Find the average of the squares:

(16 + 25 + 4 + 1) / 4 = 46 / 4 = 11.5

5) Take the square root of this number, you have your standard deviation:

sqrt(11.5) = about 3.3912
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levitate
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Joined: 17 Feb 2009
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PostPosted: Fri Feb 20, 2009 2:23 am    Post subject: Reply with quote

here is a good site:

example of calculating standard deviation
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Theodore
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PostPosted: Mon Feb 23, 2009 9:44 pm    Post subject: Reply with quote

It gives the formula, but it doesn't really explain what it means. I personally prefer the Wikipedia article, if I were going to give a link rather than posting an explanation.
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