r = cov(X,Y) / √[D(X)D(Y)]
Covariance of molecules x and y
The denominator is the standard deviation of x times the standard deviation of y.
Correlation coefficient r∈[- 1, 1]
If x and y are independent of each other, then r=0.
If r=0, then x and y are linearly independent, but not necessarily independent of each other.