Summary
The covariance of X and Y is Cov(X, Y): El[X - E(X)][Y - E(Y)I1. The correlation
is p(X, Y): Cov(X, Y)/[Var(X) Vur(Y)]l/2, and it measures the extent to which X
and Y are linearly related. Indeed, X and Y are precisely linearly related if and only if