Hi,

I am trying to understand the following simplification.

I cannot see how to get from the one step to the other.

$\displaystyle

\sum (x_i - \bar{x})(y_i - \bar{y})

$

we get

$\displaystyle

\sum (x_i y_i - y_i \bar{x} - x_i \bar{y} + \bar{x}\bar{y})

$

and then(how do they get to this step?)

$\displaystyle

\sum (x y) -n\bar{x}\bar{y} -n\bar{x}\bar{y} +n\bar{x}\bar{y}

$

and then (very obviously)

$\displaystyle

\sum (x y) -n\bar{x}\bar{y}

$

It can be seen on wolfram mathworld:

Correlation Coefficient -- from Wolfram MathWorld

I get the following.

$\displaystyle

\sum (x_i y_i) + n\bar{x}\bar{y} -n(\bar{x}\sum y_i + \bar{y}\sum x_i)

$

How does the simplification from step 2 to step 3 happen.

My simplification is not the same, and I don't see how to make it simpler.

Thanks

Regards

Craig