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  1. #1
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    sum of errors not 0




    I was just looking at some numbers (percentages, if that's useful for this question), and I've been really confused by something: my errors do not sum to zero!

    I really do not understand how this is possible - can somebody shed some light on this for me please? Surely if I take each of the following 7 datapoints, subtract it from the mean (x-xbar), and then sum together all of those errors I should be left with 0... But instead I get +- 6.66134*10^-16 (6.66134E-16 in excel).

    Numbers:
    0.678571429
    0.75
    0.767857143
    0.839285714
    0.678571429
    0.767857143
    0.517857143

    (mean = 0.714285714)


    Thanks

  2. #2
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    Re: sum of errors not 0

    Do not worry, there is not a problem i.e., theoretically, the sum of the values of the deviations of the data points from their mean is still zero. What you are observing is just a very small amount of numerical error in the computation of the sum.

    In case you do not know how to read your result, the sum is: 0.000000000000000666134.

  3. #3
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    Re: sum of errors not 0

    Quote Originally Posted by Dragan View Post
    Do not worry, there is not a problem i.e., theoretically, the sum of the values of the deviations of the data points from their mean is still zero. What you are observing is just a very small amount of numerical error in the computation of the sum.

    In case you do not know how to read your result, the sum is: 0.000000000000000666134.
    Thanks, that puts my mind at ease!

    I have never heard of this before. Would you be able to elaborate a little more? I mean how could there possibly be error in calculating the sum, and what could cause that error?

    Thanks

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    Re: sum of errors not 0

    I don't have emotions and sometimes that makes me very sad.

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    Re: sum of errors not 0


    Quote Originally Posted by Dason View Post
    Thank you!

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