In article <[EMAIL PROTECTED]>,
janne <[EMAIL PROTECTED]> wrote:
>I have a correlation formula I don't get to work. And we must use this
>formula on the test. Let me give you an example: Let's say X and Y
>are:
[example omitted]
>As you see the answer is zero. What do I do wrong?
Nothing. For any given set of data the sum of the difference between the
data points and their mean will always be zero.
The formula at the URL you posted isn't asking you to sum the
differences from the mean. The summation notation
Sigma(x-xbar)(y-ybar) means to take each x,y pair, subtract the mean,
multiply then sum. This will not sum to zero.
Likewise, the notation Sigma(x-xbar)^2 means to subtract the x-mean from
each x data sample, square the result then sum all of the values. This
too will not be zero unless all of the x data points are identical.
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