Comparing QBs across eras

Ever since I started this blog, I've challenged customary statistical measures and the notion that athletes "back in the old days" were better than they are now. (My second post, in fact, is along those lines.) Sure, Tom Brady had them fancy-schmancy 50 touchdown passes last year, but it took a real man like Bob Griese to actually quarterback his team to a perfect season -- never mind the facts that Griese threw 97 passes in 1972 (and 11 more in the Super Bowl) and that his team was #1 in rushing and #1 in points allowed that year. Clearly, Griese was the superior quarterback. Back then, guys played both ways, never got too injured to play, and rubbed dirt in their cuts -- and liked it!

So today, I decided to see if I could find a way to rate quarterbacks across generations to see if, really, Tom Brady's 50-touchdown year was "better" than Joe Montana's best season or even how it compared to old-timers like Roger Staubach and Ken Stabler -- both of whom ate nails for breakfast and could kill a man with their pinky fingers.

Directly comparing stats would be pointless. The NFL of the 70s and even early 80s, as most know, was very different, especially in the passing game. In Staubach's best year, he threw only 27 touchdown passes. Peyton Manning has had seven seasons of 27 or more TD passes. 14 of the top 20 seasons in passer rating have come since 1989. While this might mean that the quarterbacks of today are better -- despite all the rules changes that have served to open up the passing game -- it's probably better to compare quarterbacks to their peers rather than the passers of 30 years before or 30 years after their time. The NFL of 2007 is practically a different league than the one of 1977, or even 1987.

The method I'll be using is similar to ERA+, OPS+, and other measures used to compare baseball players across generations. It's basically:

(100*player stat for year X)/(league average stat for year X)

This could be used for any stat, but I'll use the familiar passer rating. What this essentially does is take a player's passer rating for a season and divide it by the league's rating for that season. A player whose rating was 90% the league's rating would have a value of 0.9. Then the result is multiplied by 100, just for ease of viewing. The above-stated player would have a PR+ (passer rating +) of 90. A league-average player would have a PR+ of 100. If the league's passer rating was 80 and a player had a passer rating of 120, his rating would be (120/80) = 1.5 * 100 = 150.

By comparing a player to his peers within a season, we should get a better idea of who truly was excellent in any given season. There are obviously other factors that go into a QB's statistical success, most notably his teammates, but that's impossible to factor out. Following is a list of all qualifying QBs since the merger I was able to find with PR+ of 150 or better, meaning they were about 50% (or more) better than the "average" QB of their day:

Player	Year	PR+
Staubach	1971	176.7
Stabler	1976	162.6
Jones	1976	161.2
Anderson	1974	155.9
Stabler	1974	154.6
Montana	1989	153.3
Staubach	1973	153.3
Griese	1971	153.3
Griese	1977	151.9
Tarkenton	1973	151.1
Staubach	1977	150.5
Brodie	1970	150.1

Well, that's something. With the exception of Montana's 1989, all the best seasons come from the 1970s. Staubach's 1971 was phenomenal. His passer rating was 104.8, compared to a league average of 59.3. By comparison, the actual best single-season passer rating, Peyton Manning's 121.1 in 2004, would have had to be 143.0 to achieve a 176.7 PR+! With the best possible rating capped at 158.3, this is virtually impossible.

Ah, but there is a caveat. Staubach threw only 211 passes in that 1971 campaign, a relatively small sample size. (This also raises the question of whether a 30-year-old guy who missed 25% of the season and threw only 325 passes is worth $60 million.) That was still good enough to rank 20th in the 26-team NFL, so he wasn't a complete fluke, but it still seems like an awfully small sample size.

Even with Staubach out of the picture, it's clear that the top of the list is dominated by 1970s quarterbacks. But here lies our second caveat: Because passer ratings were so low in the 70s, there was a lot of room for a good quarterback to excel and post a high PR+. If, for example, the average league passer rating was 110 (you know, the NFL merges with the Arena League), it would be statistically impossible for a QB to post a 150 PR+ (which would be a rating of 165) because of the cap at 158.3.

However, even taking that into account, no QB has ever approached 158.3 for a season. Even Manning's and Brady's awesome 2004 and 2007 seasons don't come close, and the 158.3 is an artificial cap rather than a natural one. For example, it's impossible for a running back to average better than 99 yards per carry, no matter how unlikely it might be. The cap on passer rating would be akin to the NFL saying no running back can go into the record books with a better than 6.0 yards-per-carry average for a season, which both Jim Brown and Barry Sanders have bested. Still, 6.0 is a practical limit, unlikely to be bested in 99.99% of seasons, as the 158.3 barrier will likely never be broken.

Still, the relatively low passer ratings of the 70s did give Staubach, Stabler, et al, more of a chance to look good relative to their peers. For the record, here are the top passer ratings, and, by extension, PR+, for each year from 1970 to 2007:

Player	Year	PR+
Staubach	1971	176.7
Stabler	1976	162.6
Anderson	1974	155.9
Montana	1989	153.3
Staubach	1973	153.3
Griese	1977	151.9
Brodie	1970	150.1
Manning	2004	149.7
Anderson	1975	149.5
Marino	1984	148.8
Young	1994	147.1
Young	1992	147
Warner	1999	145.4
Brady	2007	144.9
Montana	1987	140.6
Young	1997	139.6
Anderson	1981	139.6
Cunningham	1998	139.1
Esiason	1988	138
Young	1991	137.2
Staubach	1978	136.7
Staubach	1979	136.1
O'Brien	1985	136.1
Young	1993	135.9
Griese	2000	135
Anderson	1982	135
Kelly	1990	134.9
Kilmer	1972	133.5
Bartkowski	1983	133.5
Manning	2005	133.1
Pennington	2002	132.6
Warner	2001	132.4
McNair	2003	131.1
Harbaugh	1995	129.9
Young	1996	129.6
Kramer	1986	129.5
Manning	2006	128.7
Sipe	1980	128.2

* Daunte Culpepper's great 2004 season rates with a PR+ of 137.1, which would put it at #21 on the above list. Both he and Manning "wrecked the curve" that season; if one of them hadn't existed to drive up the league-average rating, the other would rate much higher.

* Billy Kilmer in 1972 had the lowest raw passer rating of a league leader (84.8) but is still better in PR+ than 10 other top seasons, including two of Peyton Manning's and one of Kurt Warner's.

* Both 2004 and 2007 saw the highest league average passer rating, 80.9, contributing to Manning's 2004 at #8 and Brady's 2007 at #14.

* The lowest league-average rating was 1977, which clocked in at 57.8, allowing Bob Griese to come in sixth on this list with an 87.8 rating.

* The bottom of the list is cluttered with guys who had a slightly above-average season when no other QB could manage a breakout year. Yes, Brian Sipe, Steve Bartkowski, Chad Pennington, Tommy Kramer, and Jim Harbaugh each led the league in passer rating one year. Though it should be clear from this chart that they weren't really that good -- the league around them was just mediocre. And for a guy who's only topped 20 touchdowns three times in the pass-happy early 2000s, I've always thought Steve McNair was awfully overrated.

At the least, I think this shows that maybe the best QBs of the 1970s were, if anything, a little underrated today, with the big passing numbers that everyone is throwing around. I think I'd still rather have Peyton Manning or Joe Montana as my QB than Roger Staubach or Kenny Stabler, but it's nice to see that some of those old-timers could still produce great seasons.