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Math Help - Help with variance

  1. #1
    Newbie Asylum1's Avatar
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    Help with variance

    Looking to find a simple way to find the variance of a sample data set.

    Is the only way to square the numbers,add them up and use the formula or is there a way on my calculator?

    Also I see a easy formula shown in the pic below but, Where does the x value come from I have the arrow pointing to?

    Thanks in advance.

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  2. #2
    Super Member ILikeSerena's Avatar
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    Re: Help with variance

    Hi Asylum1!

    The "x" in your formula for variance represents each value of your data set, that you are supposed to fill in one by one.

    There is probably a way on your calculator.
    Most calculators have a function to show the statistical descriptives of a sample set.
    Variance is just one of them.
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  3. #3
    Newbie Asylum1's Avatar
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    Re: Help with variance

    So your saying the only way to do this is like this?

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  4. #4
    Super Member ILikeSerena's Avatar
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    Re: Help with variance

    There are a couple of ways of doing it.

    Suppose you have the the sample 3, 4, 5.
    Its average is \bar x = 4.

    You can calculate its sample variance by the first formula you gave:

    s^2 = {(3-4)^2 + (4-4)^2 + (5-4)^2 \over 3 - 1}

    Or by the formula you gave just now (actually, I'm computing s^2 instead of \sigma^2):

    s^2 = {(3^2 + 4^2 + 5^2)  - (3 + 4 + 5)^2 / 3\over 3 - 1}

    Or by a slight modification of it:

    s^2 = {(3^2 + 4^2 + 5^2)  - 3 \cdot 4^2\over 3 - 1}
    Last edited by ILikeSerena; February 2nd 2013 at 01:41 PM.
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  5. #5
    Newbie Asylum1's Avatar
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    Re: Help with variance

    Found a real simple way to find the variance on my calculator.

    All you have to do is square the standard deviation.

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  6. #6
    Super Member ILikeSerena's Avatar
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    Re: Help with variance

    Yep. That will do the trick.

    Cheers!
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