Power rankings are always debatable. I don't buy into the gut feel methods most places use to determine their rankings, so I developed a formula a few years back that attempts to take at least some of the subjectivity out of the discussion. My approach is simple, I measure offensive and defensive efficiency based on the Yards Per Carry (YPC) and Yards Per Attempt (YPA), as well as points scored and points allowed. The formula to calculate "Team Strength" is as follows:
(YPC (offense) + YPA (offense) + Avg Pts/Game Scored) - (YPC (defense) + YPA (defense)+ Avg Pts/Game Allowed)
The formula has proven to be a pretty accurate predictor of success. Even in the first week of the 2008 season, 5 of the top 10 ranked teams were playoff bound. As with any statistic, it becomes more meaningful as the sample size grows. Usually, these become most meaningful after Week 3. In 2007, 9 of the top 10 ranked teams were playoff teams, with the lowest ranked playoff team coming in at #15. In 2008, 8 the top 10 were playoff teams, with Arizona being the lowest ranked playoff team at #19. I'm not sure any formula could have predicted their run.
If you'd like to see how teams rankings changed from 2008 to 2009, you can read more here.
This continues to be a unique season where no team can maintain the top spot for very long, and no pack of elite teams has really emerged. The prevailing opinion is the AFC is far superior to the NFC, but I'm not so sure that's how it will play out in the Super Bowl. Pittsburgh, that really looked like the class of the NFL, has fallen back a bit. Seattle, for what it's worth, moves up one spot this week. It will take many big wins to climb out of the hole they dug.
Scatter chart of the rankings. This view helps to give you a view of how teams are grouped together. You will generally see tiers of strength develop as the season wears on. Talk about a clear class system. Check out the chasm between KC and Detroit, Dallas and Buffalo.