# Math Help - why we subtract mean while calculating covariance

1. ## why we subtract mean while calculating covariance

Hi all,
First My Introduction
My Name is Vishwasrao Salunkhe
From India.
My question is
Why we subtract mean value while calculating covariance os variables.

2. Originally Posted by vishwasrao
Hi all,
First My Introduction
My Name is Vishwasrao Salunkhe
From India.
My question is
Why we subtract mean value while calculating covariance os variables.

Cov(X,Y) = E((X - E(X)) * (Y - E(Y))) ?

This is intuitive. Let us suppose that they have positive covariance. That means we expect that an increase in X is accompanied by and increase in Y. So, if x>E(X) there is a tendency to have y>E(Y) thus making the covariance positive.

Also, if x<E(X) we expect y<E(Y), and again Cov(X,Y)>0.