Have a look at Thirteen Ways to Look at the Correlation Coefficient - and especially ways 3, 4, 5 will be of most interest for you.

 - Rodgers, J.L., & Nicewander, W.A. (1988). [Thirteen ways to look at the correlation coefficient][1]. *The American Statistician, 42, 1*, pp. 59-66.  


  [1]: http://www.tandfonline.com/doi/abs/10.1080/00031305.1988.10475524