What is the equation for calculating effective cache efficiency?

The cache version of Amdahl's law is presented at http://ehcache.org/documentation/introduction.html as follows:

1 / ((1 - Proportion Sped Up * effective cache efficiency) +

(Proportion Sped Up * effective cache efficiency)/ Speed up)

On the same page, cache efficiency is said to depend on four factors, but no calculation is offered.

"Ehcache keeps these statistics for each Cache and each element, so they can be measured directly rather than estimated."

…but I need to compare statistics before and after using ehcache so it would help if I had the equation to make a like-for-like analysis.

Thanks for your help!

César.