Passer rating is one of the most widely used stat when evaluating quarterbacks and teams around the NFL. Just like the name of the stat says it only measures how good NFL quarterbacks are when passing the ball. The rating doesn’t take into account quarterback’s ability to run with the ball nor his ability to avoid any sacks. It only measures passing efficiency. It was first calculated in 1971 and therefore designed to fit passing efficiency of quarterbacks in completely different NFL era. Since 1970’s the league has changed a lot, many innovations and rule changes, especially West-Coast offense and famous ‘Mel Blount’ rule, led to an increase of league-wide passer rating. For example, in 1971 when Passer rating was first introduced, teams posted an average rating of 59.3 and in the season before the ‘Mel Blount’ rule was applied, an average Passer rating was at the lowest point of post-merger era – 57.8. After most recent ‘players safety’ rule changes the average rating made it to the highest point in NFL history last season as it climbed to 83.8. Despite the changes, the rating is still a solid measure of quarterback’s efficiency, that is passing efficiency, but the ratings from different NFL seasons should be adjusted for the era in which they’ve been recorded.
Here’s a look at steady climb of the league-wide Passer rating for the years from the AFL-NFL merger (1970) to NFL record-season (2012) which will give us a hint why those rankings should be adjusted.
From the chart above (click on image to enlarge) we can see that an average quarterback from recent years would have been an above average quarterback if compared to passers from 1970’s, 80’s and even 1990’s. In fact, an average QB from 2012 would have been a top 5 QB in 1977 and a top 10 QB in 1988. Obviously those numbers aren’t comparable. A better way to rank passers across different NFL eras would be to measure how good they were compared to a league average in years they’ve played. We can take each quarterback’s Career Passer Rating (CPR) and divide it by Average Passer Rating (APR) for the years of quarteback’s career. The result of this calculation is a % of average the quarterback was relative to the NFL. Based on those percentages we can then see if certain player was above or below average of an era in which he played. With those results we can better compare quarterbacks and their Passer ratings from different eras. For example, Joe Montana played from 1979 to 1994 and has a Career Passer Rating of 92.3, but the Average Passer Rating for the years in which Joe played (has thrown at least 1 pass) was only 72.6, that means Joe has a career rating which is 27.1% better if compared to an average rating of his era.
Before I present the best quarterback careers based on those calculations let’s first look at the most efficient passers in league history – ranked on Passer rating without any adjustments for era in which they’ve played. I took Pro Football Reference’s list of NFL Career Passer Rating leaders and left on the list only quarterbacks who played at least 50% of their careers in post-merger years. Here are the top 20 players from the filtered list.
It’s not a surprise that majority of players from above list are still active players. They play in NFL era in with is much easier to have a season with 80+ Passer rating, that’s why they are high on the list, but that doesn’t mean they are better players than the ones who played in earlier decades. One of the best quarterbacks in NFL history, Roger Staubach didn’t make it to the top 20 only because he played in an era in which it was much more difficult to have a Passer rating of, let’s say 80, a rating which is nowadays an average rating.
For a better quarterback comparison across NFL eras I put up a table of top 20 quarterbacks in which I sorted players based on % above average Passer rating of the era in which they’ve played.
A lot more Hall Of Fame players make the list, led by Roger Staubach, Philip Rivers falls from 6th to 18th place, Tony Romo from 5th to 16th and many active players listed on the first list disappear from the era-adjusted list. It doesn’t ‘adjust’ the fact that the rating was designed for a different era or the way the rating is calculated. That’s why the presented adjusted list isn’t a perfect list of NFL best quarterbacks from 1970-2012, but if you want to rank player’s careers based on Passer ratings I think this is a better way compared to the list of Passer ratings without any era adjustments.
In the comings days I’ll post a similar comparison for the NFL best Single-season Passer ratings.