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Math Help - whats the equation for standard deviation?

  1. #1
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    whats the equation for standard deviation?

    as stated in post heading. *equation meant to be formula lol

    Im confused, could somebody give me the forumla for standard deviation? x
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  2. #2
    GAMMA Mathematics
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    Quote Originally Posted by leaaa View Post
    as stated in post heading. *equation meant to be formula lol

    Im confused, could somebody give me the forumla for standard deviation? x
    \sigma = \sum_1^n \sqrt{\frac{(x_i - \bar{x})^2}{n}}
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  3. #3
    GAMMA Mathematics
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    Quote Originally Posted by colby2152 View Post
    \sigma = \sum_1^n \sqrt{\frac{(x_i - \bar{x})^2}{n}}
    Keep in mind that is for a population set. For a sample, you must divide by n-1!
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  4. #4
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    Quote Originally Posted by colby2152 View Post
    \sigma = \sum_1^n \sqrt{\frac{(x_i - \bar{x})^2}{n}}

    No the sample SD:

    <br />
s = \sqrt{\frac{1}{n}\sum_1^n (x_i - \bar{x})^2}<br />

    Or for the estimator of the population SD

    <br />
s = \sqrt{\frac{1}{n-1}\sum_1^n (x_i - \bar{x})^2}<br />

    or sample SD for grouped data:

    <br />
s = \sqrt{ \frac{\sum_1^n n_i (x_i - \bar{x})^2}{\sum_1^n n_i}}<br />

    where there are n groups with group marks x_i and frequency count n_i.

    ZB
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  5. #5
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    Quote Originally Posted by colby2152 View Post
    Keep in mind that is for a population set. For a sample, you must divide by n-1!
    Where in this context ! is of course an exclamation, NOT a factorial.
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