I asked this question this question of my high level HR wife this morning. She didn't really have much of an answer other than - too long or quite awhile. So before work I sent Google off to do what it does best. Below is the starting point.
Here
As an open discussion go ahead and see what you can see. Anything stand out more than another? Industries, fields etc? I am asking an open ended question as much of what was found is quite interesting.
-b/eads