NFL Stat Analysis: Opposition Adjusted Quarterback Rating

MIAMI - SEPTEMBER 21:  Quarterback Peyton Manning #18 of the Indianapolis Colts points out to his wide receiver against the Miami Dolphins at Land Shark Stadium on September 21, 2009 in Miami, Florida. The Colts defeated the Dolphins 27-23.  (Photo by Doug Benc/Getty Images)
Luis AlbertoCorrespondent ISeptember 25, 2009

Opponent Adjusted Quarterback Rating: Week Two

I recently put together a regression model to determine the factors that most drive the number of points a football team scores in any given game.  It's a work in progress, but the factors I looked at were:
  • Yards per attempt (Y/A)
  • Interception Percentage
  • Yards/Rush
  • Average Y/A yielded by opponent
  • Average points yielded by opponent
Of the variables above, Y/A was, by the far, the strongest—followed by interception percentage.  The other three were pretty close in importance.
You'll notice that a quarterback has a direct impact on two of the five. With that in mind, I decided to create a quarterback rating system that looks primarily at the factors of Y/A and interception percentage. 
Further, because a quarterback's performance is obviously affected by their opponent, I added an element that accounts for the quality of the opponent's defense
The formula for the rating, which I'm going to call the Opposition Adjusted Quarterback Rating (OA Quarterback Rating) until I can think of a cooler or funnier name.
The formula was basically:
  • Y/A minus the opponent's average Y/A yielded PLUS
  • Int percentage minus the opponent's average Int percentage yielded
A few notes.  Because the season is only two weeks old, the "Opposition Stats"—the stats that were used for Y/A and Int percentage yielded—were from all of 2008 and the first two weeks of 2009.  So, there is a margin of error there.
Also, when calculating the "Opposition Stats", the metrics from the game against the current quarterback was not counted.  (i.e., if Jay Cutler is playing the Raiders, the "Opposition Stats" are from all of the games in 2008 and 2009 except for the one being played against the Raiders).
By the way, this is all a work in progress.  As I get more information I will layer it in.
Below are the OA Quarterback Ratings for 2009 through Week Two.  See the 2008 rankings here.
OA Quarterback Ratings: Through Week Two 2009

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