Quick Standard Deviation Question

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  1. Supernova123's Avatar
    1 02-03-2010  00:36
    • Junior Member
    • Posts: 37
    Quick Standard Deviation Question
    I have sigma x = 1810.8, sigma x^2 = 156460.1 for a sample of 25.

    so we can work out the mean by sigma x / 25

    how would i work out the standard deviation, thanks
  2. Chwirkytheappleboy's Avatar
    2 02-03-2010  00:47
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    • Location: London
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    Re: Quick Standard Deviation Question
    If you check out Wikipedia you'll find a few variations of the standard deviation formula. I think the one that will be most useful to you is this:

    \sigma = \sqrt{\dfrac{1}{N}\left(\display style \sum_{i=1}^Nx^2_i\right)-\bar{x}^2}
  3. Mathematician!'s Avatar
    3 02-03-2010  01:09
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    Re: Quick Standard Deviation Question
    (Original post by Chwirkytheappleboy)
    If you check out Wikipedia you'll find a few variations of the standard deviation formula. I think the one that will be most useful to you is this:

    \sigma = \sqrt{\dfrac{1}{N}\left(\display style \sum_{i=1}^Nx^2_i\right)-\bar{x}^2}
    The formula may vary slightly (the \frac{1}{N} becoming \frac{1}{N-1}) so as to prevent dividing by 0 (i.e. is valid for a small sample).
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