In this series of posts I'm going to build a better quarterback rating system. The system will be try to isolate the passing stats that the QB alone is primarily accountable for. The stats will be efficiency stats in that they are in terms of attempts. The system will also attempt to exclude redundancy stats.
The official Passer Rating system includes co-dependent factors such as TDs, interceptions, and completion percentage. But an accurate QB will tend to have both a high completion rate and high TDs. The passer rating, therefore, double counts accuracy. Further, a QB's passing TDs may be due to his defense's ability to get the ball turned over to him in his oppenents' territory, or due to an effective running game, as much as due to his own ability. The goal is to isolate what the QB is truly responsible for and filter out what the QB does not control.
The system will include completion percentage, interceptions per attempt, and sack yards per pass attempt. Although interceptions and sacks are not solely attributable to the QB, the stats imply that the QB is overwhelmingly responsible for them. Take the case of McNair in Baltimore. After replacing Kyle Boller, Baltimore went from one of the league's worst sack rates to one of the best. The rest of the offense, including the offensive line, was completely identical.
Each stat in the system will be translated into team wins by the efficiency win model previously established. In the first post we'll rank quarterbacks in terms of their 2006 regulare season completion percentage. We'll compute how many percentage points above or below average each QB was last year. All other factors being equal, every additional point of completion percentage brings an extra 0.18 wins to a team on average. Therefore we can compute how many wins each QB contributed to his team by his completion percentage alone.
(Only QBs with more than 100 attempts are considered.)
|Player||Comp Pct||Pct > Avg||Wins Added|
In the next post, I examine interception rate. Then in the third part of this this article, I'll look at sack yardage rate. Finally, I'll sum the wins added for each QB to produce a more valid passer rating system.