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Stat Sheet Misconceptions: Passer Rating

Before we move on to statistics for other positions, I think it’s necessary to examine my least favorite for quarterbacks, the Passer Rating. This number combines all of the basic statistics that are used to measure a quarterback’s passing performance into a single final figure, designed to be the ultimate evaluation for comparison's sake. As you can see here, the Passer Rating is not the easiest number to make sense of.

According to NFL.com, “in rare cases” a quarterback will have a rating over 100. In 2010 alone, Tom Brady, Philip Rivers, Aaron Rodgers and Michael Vick all accomplished this feat and ended with ratings of over 100 for the season. Vince Young was also close to this “elite” level, finishing 5th on the list with a rating of 98.64, but I doubt many teams will be fighting to bring him aboard next season.

Here we will try to make their complex formula a little easier to handle, and then we'll take a look at the flaws of the individual parts of the formula, the flaws of the formula itself, and why we can’t use passer rating to compare eras.
 

What Goes Into It

When websites attempt to explain passer rating, they’ll often have a step by step process that isn’t very easy to follow. However, if you’re willing to do some algebra and make some assumptions, the formula is simpler and looks like this:

The 42 quarterbacks with the most attempts in 2010 fit the assumptions, and, in general, we don’t need to worry about them when we’re looking at a large number of attempts. However, in the interest of completeness, the assumptions are: completion percentage is between 30% and 77.5%, yards per attempt are between 3 and 12.5 yards, touchdowns are thrown on less than 11.875% of throws, and interceptions are thrown on less than 9.5% of throws. If a number is above a maximum or below a minimum, than you assume it’s the maximum or minimum value and it still works out.
 

The Problem With What Goes Into It

We’ve already seen that completion percentage is imperfect, and while interceptions per attempt are better than just plain interceptions, many of the same problems we discussed remain. Yards and touchdowns, in my opinion, aren’t as bad, but are both still largely dependent on situation and supporting cast. Putting them all together in a formula doesn’t make them any less flawed, so the Passer Rating incorporates all of the problems mentioned in the past two articles plus some.
 

What’s Worth More?

The values that were used to determine the passer rating were chosen based on league averages from years ago, but even then, they didn’t make sense. Here is an example of why:
 

Quarterback A throws three straight passes, completing them each for three yards. Plugging three completions, nine yards, three attempts, zero touchdowns, and zero interceptions into the equation above, and you get a quarterback rating of 97.92, which is a very good rating.

Quarterback B throws three straight passes, the first two land incomplete, and the third is caught for a 30 yard gain. Putting those numbers into the equation, you get a quarterback rating of 71.53. In the first situation, the offense is now facing fourth down, where in the second the ball just went 30 yards down field.

 

The first quarterback has a rating of an all pro, while the second has the rating of someone fighting for their job.
 
The equation is basically saying that a completion is worth as much as 20 yards, a touchdown is worth as much as 80 yards, and an interception is worth -100 yards. It makes sense that touchdowns are worth more than yards, and interceptions are negative, but, as the example illustrates, completions are very much overvalued because in reality, they only help if they gain yards.
 
The relative values of touchdowns and interceptions don’t make sense either. You already know that I believe the interception is overvalued as an indicator for QBs. As for touchdowns, in a game, it doesn’t matter if a quarterback were to run for one or pass for one, yet there would be a significant difference in their passer rating. I would argue a touchdown is overvalued as well.
 

Historic Comparison

Because of an increased number of games played in the regular season, rules opening up the passing game, and offenses simply opting to pass more often , the all-time quarterback leader boards are slowly being taken over by more recent players. This is more true for Passer Rating than any other statistic.
 
A look at the all time leaders shows 25 of the top 30 QB’s by Passer Rating to be players who are either still playing or who ended their carriers in the past decade. Over the years, completion percentage, yards per attempt and touchdowns have all risen while interceptions have dropped; evidence that the environment today’s QBs are playing in is significantly different than that of years past. With other statistics, you can account for era to make a more fair comparison between quarterbacks who didn’t play at the same time, but for Passer Rating this doesn’t make sense.
 
Chad Pennington is currently ranked as the 12th best quarterback of all time in terms of Passer Rating while Hall of Famer Joe Namath ranks 182nd. Clearly we have a problem.
 

Closing Thoughts

While we will never get rid of completion percentage or interceptions, the passer rating is something I sincerely hope is eliminated from stat books someday. The difference being that completions, attempts and interceptions are all things that we count, and it’s just the way the numbers have been interpreted that has become flawed.
 
The purpose of Passer Rating is to provide one number to use for comparing relative passing success among quarterbacks, but there are better ways to do this. Most football statistics websites have developed a version of their own by re-working the current formula. We think the PFF pass grade for quarterbacks is the best tool to use when evaluating and comparing passing performances. Whatever way you look at it though, the NFL’s Passer Rating is out of date and is no longer needed.
 

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