Last year, I wrote a six-part series on adjusting passer ratings for era.

Background reading:

Part I

Part II

Part III

Part IV

Part V (Career Passer Ratings)

Part VI (Single Season Ratings)

Passer rating is made up of four variables: completion percentage, yards per attempt, touchdown percentage, and interception percentage.  The reason passer rating needs to be adjusted for era? When it was derived, in order to get an average rating in each of the four variables, a passer needed to complete 50% of his passes, average 7.0 yards per pass, have a touchdown rate of 5%, and have an interception rate of 5.5% (yes, INT rates used to be higher than TD rates).  But those numbers — 50%, 7.0, 5%, 5.5% — were pegged in the 1970s and are not dynamic.  However, I came up with a formula that matches the intent of passer rating but just ties the variables to the league average in any given season. You can get the formulas and read more background in the linked posts.

Now, in 2017, the four averages were 62.1%, 7.02, 4.24%, and 2.46%.  One thing to keep in mind: these adjustments will not change the order of passer ratings in a given season.  So Alex Smith, Drew Brees, Tom Brady, Carson Wentz, and Jared Goff remain the top five; the way the formula works, it just subtracts a fixed amount from each passer’s actual passer rating.  In 2017, that amount was 20.26 during a poor passing season; it was 22.59 lower than actual in 2016.

Below are the 2017 passer ratings, with the rank being the historical rank from 1936 to 2017:

Kizer had the second worst era adjusted passer rating of any QB since 2000. The bottom five? JaMarcus Russell in 2009 (33.66), DeShone Kizer in 2017 (40.25), Jimmy Clausen in 2010 (40.96), Akili Smith in 2000 (41.44), and Andrew Walter in 2006 (42.05).