Thursday, December 19, 2013

Omission of information on sacks from the QB rating system

This was reprinted from my sports blog.   The NFL QB rating system is basically a composite index.   I believe it would be improved by including information on sacks.   

Issue One:  Why might the omission of information on sacks from the QB rating system lead to a misleading QB comparison?

Answer:  Some quarterbacks may avoid an interception by holding on to the ball too long and getting sacked.  The impact of the omission of information on sacks from the QB rating system can illustrated by comparing 2011 passing statistics for Aaron Rodgers, the top rated passer in the regular season to the passing statistics of Drew Brees the QB with the second highest rating. 

The statistics in Table on reveal that in 2011 Aaron Rodgers outperformed Drew Brees in three of the four passing statistics that make up the NFL QB rating system.  Rodgers had the superior numbers for yards per attempt, touchdown percentage and the interception percentage, while Brees had the better number for the completion percentage statistic.  However, in 2011 Drew Brees had the lowest sack percentage in the NFL while Aaron Rodgers had a sack percentage at approximately the 60th percentile.

An alternative QB rating index with a fifth component the sack percentage is created.  The formula for the alternative QB rating system is the sum of the five components divided by 7.5.  This alternative QB rating system, like the official system has a maximum possible value of 1.583.  The estimate of the interception component for Aaron Rodgers is the average of the value of the median values for the four official components and that the estimate of the interception component for Drew Brees is the average of the best value of the four official components.  (This assumption is conservative since Rodger’s sack percentage was above the median)

The alternative QB rating index with sack percentage included as a fifth component results in a QB rating of 114.8 for Aaron Rodgers compared to a QAB rating of 113.5 for Drew Brees. 


Comparing Rodgers and Brees 2011 Regular Season
Rodgers
Brees
Attempts
502
657
Completion Percentage
68.3%
71.2%
Yards per attempt
9.2
8.3
Touchdown %
9.0%
7.0%
Interception %
1.2%
2.1%
QB rating check
122.5
110.6
Sack %
7.2%
3.7%
Percentile Sack %
59.3%
0.0%
QB rating with adjustment for sacks
114.8
113.5

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