I also came across an article that was relevant to this thread. There was a study conducted with an article published by the journal,
Labour Economics. Unfortunately, the study itself has to be purchased in order to view.
http://newsinfo.iu.edu/web/page/normal/17626.html
Essentially what they found was this: The race of a coach has not impacted their chances of getting a head coaching job in today's NFL, and the Rooney Rule isn't responsible for the increase in hiring of minority candidates.
What has led to the increase in the hiring of minority candidates? Success at coordinator positions and younger age.
That goes back to my earlier post in this thread - If you wanna see more minority head coaches, you'll need more minority coaches in OC and DC positions, which is naturally happening anyway.
Plus, for the most part, it takes a very long time to become a HC in the NFL. Given the fact that there weren't many minority coaches to begin with the NFL back in the 70's and 80's, it would make sense that the NFL didn't really have more minority head coaches by the late 90's or early 00's.
Andy Reid started coaching football in the early 80's, and didn't get a HC job until 1999. Bill Belichick was a coach for 16 years before becoming a HC. I share these examples because if most coaches in all positions back in the 70's and 80's were white, and it look a lot of them over 15 years to become a head coach, it, of course, would make sense that most head coaches would be white. As minority coaches in lower level coaching positions become more common, they've been moving their way up into coordinator positions, and ultimately head coaching jobs. It's just a long process and you won't see the impact over night.
Essentially, I agree with this:
"You need to expand the pool of available talent, and the way to do that is to get more minority coaches involved early on," Walker said.
Often, he said, former players enter the coaching profession by serving as volunteer assistants while attending graduate school, a route that may be less open to minorities. If the NFL wants to expand the future talent base of coaches, he said, it might consider providing financial and other support for African-Americans and Hispanics who want to learn coaching after college.