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Standard Deviation Calculation

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1 Standard Deviation Calculation on Thu Jan 28, 2010 7:54 pm

Hey all:

As the chem test is approaching tomolo, though Connie said she won't ask any math questions, there's still the possibility for her to ask us to do a standard deviation calculation. So here's a quick math tutorial!!

(Please pardon me this will have some excel component, but do look at the equation in the chem lec 2)

Standard Deviation Equation: SQRT(E(x - x bar)^2/(n-1))

The E is epsilon or Sum of (x - x bar)^2,
x bar = mean,
x = data point
n = # of data points

Here's an example:
Given data set:
3
8
12
6

Mean = (3+8+6+12) = 29/4 = 7.25

So now the E(x - x bar)^2 will look like this (3 - 7.25)^2 + (8 - 7.25)^2 + (6 - 7.25)^2 + (12 - 7.25)^2 = 42.75

We have 4 data sets so n = 4

Now sub it into the formula: SD = SQRT(42.75/(4 - 1)) = SQRT(42.75/3) = 3.775

For CV = 3.775/29 * 100% = 13%

Hope Everyone find this useful and ask if you have trouble going over this!!

Cheers,
Ash

PS: Dan found this website if you still dont understand what I have talked about http://hubpages.com/hub/stddev

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2 Re: Standard Deviation Calculation on Thu Jan 28, 2010 9:37 pm

Thanks Ashley,


Good refresher!

Pat

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