Hello,
I'm generally comfortable with the idea of covariance, but there's a way of writing covariance that i don't understand.
Could someone please explain how we get to the second way of writing covariance above?
I naively would have just multiplied what look like two binomials in the first expression, which of course would not produce the second expression.
Thanks for the help
Ben
I think your missing something in the equation or formula, it should be written as:
E { ( X - meanX) ( Y - meanY) }
E = Expected = the mean of some expression
so it's the mean value of the product (multiplication) of X minus its mean and Y minus its mean
so it can be expressed as the average value " E " of the multiplication of X minus its mean by Y minus its mean
and that's why when we convert it to real data, we take the sum of all (X-meanX)(Y-meanY) and divided it by N to average it
I think the expression on top is just a mathmatical way to express a mean value using " E "
but the technical form is the one ur familiar with