Background reading (Part I, Part II, Part III, Part IV, Part V: Career Era-Adjusted Passer Ratings Through 2016, 2017 Era-Adjusted Passer Ratings). You can also view the single-season era-adjusted passer ratings here.
The NFL’s passer rating formula can be broken down into the following.
A = (Cmp% – .30) * 5
B = (Y/A – 3.0) * .25
C = TD% * 20
D = 2.375 – Int% * 25
Passer Rating = 100 * (A + B + C + D) / 6
Let’s use Tom Brady as an example. He has a completion percentage of 63.93 (making A = 1.696), a yards per attempt average of 7.514 (making B = 1.128), a TD percentage of 5.54% (making C = 1.108), and an INT percentage of 1.82% (making D = 1.921). If you sum A, B, C, and D, multiply by 100, and divide by 6, you get 97.6, which is Brady’s career passer rating.
Last year, I derived the formula to create era-adjusted passer ratings. This is necessary because the league averages in these variables — particularly completion percentage and interception rate — have changed dramatically over the last 50 years. For example, when passer rating was created in the early 1970s, the average completion percentage was 50%. So instead of taking each passer’s completion percentage and subtracting 0.30 (before multiplying by 5), we take each passer’s completion percentage and subtract from that the league average in a given season minus 0.20. This makes a completion percentage of 60% in the 1970s equivalent to a completion percentage of 70% when the league average completion rate is 60%.
We can do that for all the four variables, and keep the same formula/structure largely in place.
Here are the new formulas for each of the four variables:
A = (Cmp% – (League_Avg_Cmp% – 0.20) ) * 5
B = ( Y/A – (League_Avg_Y/A – 4.0) ) * .25
C = TD% * 20 + (1 – 20 * LgAvgTD_Rate)
D = 2.375 – (Int% * 25 + (1.375 – 25 * LgAvgINT_Rate) )
Then we sum A through D, multiply by 100, and divide by 6. The table below shows the career era-adjusted passer ratings for the 186 passers with at least 1,500 attempts. Here is how to read the table below. Otto Graham is the career leader in era adjusted passer rating (this analysis includes AAFC and AFL data — we are only adjusting for era in this analysis, not strength of league). He threw 2,626 passes in his career, began in 1946 and finished in 1955, had an actual passer rating of 86.6, and an era adjusted passer rating is 95.2. Graham, of course, is in the Hall of Fame.
Much of my analysis this time last year won’t change, of course, so I’m reprinting some of it here. Graham and Len Dawson both rank in the top 4, and both benefited to some extent by player in expansion leagues with weaker competition for the early parts of their careers. Seeing Sid Luckman and Sammy Baugh in the top three reflects the way those two passers dominated their era.
One fun thing to do is to sort by attempts to see who stands out. Brett Favre ranks 44th in era adjusted passer rating, Peyton Manning is 11th, and Drew Brees is 19th. Dan Marino is 25th, but like Manning, Marino is harmed a bit by ignoring his outstanding sack rate. Tom Brady ranks 13th, while John Elway is down at 74.
Eli Manning is way, way down at 126 — a hair below his father, Archie Manning (who is at 113). In fact, Manning, with a 65.1 era-adjusted passer rating, has a below-league average passer rating. By definition, the average passer rating in every season is 66.7 in this formula (400/6). Players with a 65.1 era-adjusted passer rating include Bledsoe, Plunkett, Tannehill, and Bradford.
The five lowest HOF QBs on the list are John Elway, Terry Bradshaw, Bobby Layne, Joe Namath, and George Blanda. Namath had three terrible years when he was washed up, and was outstanding at avoiding sacks, which is why he’s underrated; given Namath’s focus on big plays and avoiding sacks, he’s never going to fare well in passer rating, but his era adjusted rating does rise to 72.9 if you remove his final three seasons.
Blanda was another guy who was incredible at avoiding sacks, and who focused on big plays rather than completion percentage (whereas a contemporary like Dawson’s game was much more about completion percentage and avoiding interceptions). He also is perhaps the weakest quarterback in the Hall of Fame, although his era-adjusted passer rating is still above league average. I’ve written before about the stats of Bradshaw and Elway; Layne’s stats have often underwhelmed me, but Brad Oremland has written some good words about him.
On the other side, you won’t be surprised to see Ken Anderson — whose game was well-designed for passer rating — excels here. Other than Frankie Albert, who played most of his short career in the AAFC, he has the best passer rating of any retired player not in the HOF. Kurt Warner is right there, too (though his stats are arguably inflated, too), with Daryle Lamonica (a player whose game was decidedly not passer rating-friendly) and Bert Jones not far behind. Tony Romo is not yet eligible, of course, but he looks great in this analysis as well (of course, Romo has the 4th-best actual passer rating of all time). Aaron Rodgers, who has the best passer rating ever, ranks 7th once we adjust for era.
What stands out to you?
