Let's play a little game of blind résumé. You can pick which NFL defense had a better season in 2011, based on a few basic season level stats. Team A allowed only 272 yards per game -- the best in the NFL -- and gave up 227 points, also the best in the league. Team B allowed 312 yards per game and 363 total points. Seems like an obvious one, right? Yards allowed and points given up are generally the two most cited statistics when measuring team defense.
However, what if I told you the team that allowed 50 more yards per game also forced twice as many turnovers? And what if that same team that allowed 136 more points had an offense that lead their conference in giveaways and put their defense in the worst average starting field position in the league due to those turnovers?
By now hopefully you can tell I'm not speaking hypothetically. These teams were the Pittsburgh Steelers (Team A) and the New York Jets (B) from last season. The Steelers led the league in what is typically known as "total defense" (yards allowed) and scoring defense (points allowed). The Jets were fifth in total defense, but also forced 16 more turnovers than Pittsburgh while inarguably having a more self-cannibalizing offense to deal with.
The point of all this is to say it is hard to determine defensive quality using basic stats. For every stat you find there will be another one that contradicts it. To properly evaluate defenses -- or offenses for that matter -- you must take into account all of this information and relate it to preventing points given the situations defenses were put in. And when you do that with the early results from Week 1 in 2012, you find that the Houston Texans once again appear to have a dominant defensive unit.