In 2006, I took a stab at ranking every quarterback in NFL history. Two years later, I acquired more data and made enough improvements to merit publishing an updated and more accurate list of the best quarterbacks the league has ever seen. In 2009, I tweaked the formula again, and published a set of career rankings, along with a set of strength of schedule, era and weather adjustments, and finally career rankings which include those adjustments and playoff performances. And two years ago, I revised the formula and produced a new set of career rankings.

This time around, I’m not going to tweak the formula much (that’s for GQBOAT VI), but I do have one big change that I suspect will be well-received. Let’s review the methodology.

Methodology

We start with plain old yards per attempt. I then incorporate sack data by removing sack yards from the numerator and adding sacks to the denominator. To include touchdowns and interceptions, I gave a quarterback 20 yards for each passing touchdown and subtracted 45 yards for each interception. This calculation — (Pass Yards + 20 * PTD – 45 * INT – Sack Yards Lost) / (Sacks + Pass Attempts) forms the basis for Adjusted Net Yards per Attempt, one of the key metrics I use to evaluate quarterbacks. For purposes of this study, I did some further tweaking. I’m including rushing touchdowns, because our goal is to measure quarterbacks as players. There’s no reason to separate rushing and passing touchdowns from a value standpoint, so all passing and rushing touchdowns are worth 20 yards and are calculated in the numerator of Adjusted Net Yards per Attempt. To be consistent, I also include rushing touchdowns in the denominator of the equation. This won’t change anything for most quarterbacks, but feels right to me. A touchdown is a touchdown.

Now, here comes the twist. In past year, I’ve compared each quarterback’s “ANY/A” — I put that term in quotes because what we’re really using is ANY/A with a rushing touchdowns modifier — and then calculated a value over average statistic after comparing that rate to the league average. For example, if a QB has an “ANY/A” of 7.0 and the NFL average “ANY/A” is 5.0, and the quarterback has 500 “dropbacks” — i.e., pass attempts plus sacks plus rushing touchdowns — then the quarterback gets credit for 1,000 yards above average.

This time around, I’m going to incorporate strength of schedule by comparing each quarterback in each game not to league average, but to the “ANY/A” allowed by the opposing team in each of their other games. Add up the Value relative to the defense in each game of each season, and you get season grades. This step combines a SOS and era adjustment all in one, and frankly, I’m not sure why it took me so long to get around to this.

There are three final steps. After creating season grades, we need to include two more statistics and then make one last adjustment. First, we subtract for “net fumbles” lost by the quarterback, which represents the number of fumbles by a quarterback minus the number of fumbles he recovered. Based on prior research, a net fumble is worth about -30 yards, so -30 is subtracted for each net fumble. I calculated the average fumbles lost per “Dropback” by quarterbacks in each year (which was just north of 1.0% for most years) and then gave each quarterback credit (or a penalty) for their net fumbles above/below average.

We also must add a rushing component. I have never figured out a good way to handle quarterback rushing, but what I’ve done in the past is to add all quarterback rushing yards over 4.0 yards per carry. So 500 yards on 100 carries goes down as +100. That’s not very scientific, but the results have been noncontroversial, so I’ll continue to use it until someone suggests something better.

Finally, I made adjustments for non-16 game NFL seasons. For seasons with fewer than 16 games, all stats have been pro-rated to 16 games. And for the first five years of the AFL, I reduced the value of quarterback statistics.

Last time around, Tom Brady’s 2007 season ranked not just third, but a somewhat distant third to Dan Marino 1984 and Peyton Manning 2004. As it turns out, the SOS adjustment changes that. The table below shows the top 100 quarterback seasons since 1960. Let’s walk through Brady’s ’07 to guide you through the table. In 2007, Brady threw for 4,806 yards and 50 touchdowns, while recording just 8 interceptions, 21 sacks, and 128 sack yards lost. He had a “Relative ANY/A” of +3.63 (this includes the rushing TD bonus). He had a harder than average schedule, although that’s already been factored into his “RANY/A” (I’m including the SOS column for reference only). Brady had 601 dropbacks, and since he had fewer fumbles than average, gets an 88 yard fumble value bonus (but no rushing bonus). Add it up, and Brady produced 2,270 yards of VALUE over average, the most of any quarterback in any season since 1960.

The table is fully sortable and searchable. Some thoughts:

Peyton Manning leads the way with 11 top-200 seasons. Brady, Marino, Steve Young, Drew Brees, and Fran Tarkenton are in a five-way tie for second with 7 top-200 seasons.

Players who are eligible but not in the Hall of Fame with the most top-200 seasons: Ken Anderson (5), John Brodie (4), Boomer Esiason (4), Daryle Lamonica (4).

San Francisco leads the way with 17 top-200 seasons: seven by Young, five by Joe Montana, four by Brodie, and one by Jeff Garcia. The Chargers are second with 12 such seasons, with Brees and John Hadl (!) each contributing one year, and Fouts and Philip Rivers delivering the rest.

And now, the huge caveat: It’s important to remember that this is just a measure of each team’s passing game, assigned to the quarterback on the field for those plays. Obviously the quality of the offensive line, the ability of the receivers, the versatility of the tight ends and running backs, the philosophy of the coaches, the strength of the schedule, and good old randomness have a significant impact on the above numbers. The reason for these posts is to accurately measure quarterback statistics, and nothing else. Once we have strong measures of QB performance, we can then judge QBs based on how much of their success (or lack thereof) we want to assign to the QB and how much to other people/factors.

And, of course, even if supporting casts are the same, numbers don’t tell the full story. The point here is simply to get the most out of the numbers we have. Anyway, I’m sure this gives you more than enough to chew on. Leave your thoughts on the methodology and the single-season leaders here; tomorrow, we get to the career list.