Can we track this?

Steve Spagnuolo Rob Ryan, Greg Williams. All are defensive coordinators, and all coached some of the worst defenses in NFL history, which also happened to be Saints defenses. Now we have Dennis Allen coaching the defense, and things have started bumpy.

Would it be fair to compare these four guys during the season, and see if it's coaching or if it's something more?

What parameters would you use in comparing the 4?