There are countless ways to evaluate quarterbacks, but one of the most underrated traits is consistency.
A quarterback who consistently keeps his team in games is sometimes better than the one who carries it in a few games, but costs it a few others.
To determine who this year's most inconsistent quarterbacks were, I evaluated their performance based on how consistent their Total QBR was from game to game.
In the following slideshow, the 27 quarterbacks with at least 10 qualifying QBR games are ranked based on their average variance in QBR.
This was calculated by comparing their full-season QBR to their QBR in each individual game.
Let's use Nick Foles as an example. Foles' Total QBR for the season was 69.0. In Week 17 against the Dallas Cowboys, he posted a QBR of 40.8. This gives him a QBR variance of 28.2 for that game.
Total QBR: 31.9
Average Variance: +/- 12.51
Consistency isn't always a good thing, and in Chad Henne's case, it's exactly why his NFL career may be over.
Henne's Total QBR of 31.9 ranked dead last among the qualifying quarterbacks, and it wasn't due to just a few poor performances.
Henne posted a QBR above 50 just once this season (Week 14 versus Houston) and was below 25 on four occasions.
Total QBR: 55.4
Average Variance: +/- 14.09
Ryan Fitzpatrick was a model of consistency, albeit with a fairly mediocre performance.
It could be argued that Fitzpatrick was the perfect game manager this year. He never carried the Tennessee Titans to victory, but he also never caused their defeat.
In 10 starts, Fitzpatrick never posted a QBR over 76, but he also had just one performance below 30 (29.7 against the Seattle Seahawks).
At the age of 31, Fitzpatrick has established himself as a career backup, but he's also among the best backup options in the league.
Total QBR: 61.1
Average Variance: +/- 14.4
The one bright side to the Atlanta Falcons' disaster of a year was that Matt Ryan continued to play at a consistently high level.
Only four of Ryan's starts dipped below the 50-point mark in QBR. Additionally, some of his best performances of the season came against the New Orleans Saints and San Francisco 49ers.
With an improved and healthier supporting cast, there's no reason to believe Ryan can't return the Falcons to an elite level in 2014.
Total QBR: 82.9
Average Variance: +/- 15.0
Among the 27 qualifying quarterbacks on this list, Peyton Manning topped them all in total QBR, but one miserable game against the New England Patriots knocked his consistency rating down.
Manning's 28.1 rating against the Patriots skewed his QBR variance down significantly, but it was his only game under 50.
It's worth noting that the Denver Broncos lived and died by Manning's performance. Three of his four worst QBR performances all resulted in Broncos losses.
Total QBR: 62.0
Average Variance: +/- 17.06
For a second-year quarterback Andrew Luck's consistency was remarkable.
Luck lacked the dominant performances of some of the elite quarterbacks in the league and managed just one QBR performance over 85. But his impressive consistency kept the Indianapolis Colts in nearly every game.
In the 10 games in which Luck topped 60 in QBR, the Colts went 9-1. In the other six games, they were 2-4.
Total QBR: 71.7
Average Variance: +/- 17.19
The San Diego Chargers barely snuck into the playoffs, but this was arguably Philip Rivers' most impressive performance of his career.
Among our 27 qualifying quarterbacks, Rivers only trailed Peyton Manning in Total QBR, and his performance was remarkably steady.
Rivers posted a QBR above 80 six times, all resulting in Chargers victories. And only once did his QBR fall below 40, way back in Week 1 in a loss to the Houston Texans.
Total QBR: 37.3
Average Variance: +/- 17.27
Consistency wasn't a positive for Matt Schaub in 2014, as he limped through the worst season of his career.
Schaub's performance peaked with a QBR of 63.5 against the St. Louis Rams, which still resulted in just a 13-point effort for the Texans.
He also managed to drop below 20 on three occasions, bottoming out with a 4.9 QBR against the 49ers in Week 5.
Total QBR: 45.8
Average Variance: +/- 17.73
Ryan Tannehill's QBR was slightly below the average mark of 50, but his consistency is encouraging for the Miami Dolphins.
While Tannehill topped 70 just once (against the Patriots), his QBR fell between 50 and 70 on seven other occasions. In total, the Dolphins went 6-2 when Tannehill's QBR was 50 or above.
Unfortunately for Tannehill, he also managed a few duds, which dragged both his overall and consistency ratings down considerably. His two worst QBRs both came against the Buffalo Bills, with performances of 15 and 3.2.
Total QBR: 59.5
Average Variance: +/- 17.75
Despite all the hate, Tony Romo ranks in the upper third of the league in Total QBR and in terms of his consistency.
Romo did drop below 40 twice (Week 1 in a win against the New York Giants and Week 10 in a loss to the Saints), but he balanced it out with a few dominant performances as well.
Perhaps the best evidence of all that the Cowboys' issues are anything but Romo is the fact his QBR had absolutely no impact on their wins and losses.
The Cowboys went 3-3 in Romo's six best performances, including a loss during a 92.1 QBR effort against the Broncos. They also went 3-3 in his six worst games, including a win over the Giants despite a 27.1 QBR.
Total QBR: 36.5
Average Variance: +/- 17.93
Among the 27 quarterbacks on our list, only Chad Henne and Geno Smith posted a worse QBR than Eli Manning—not exactly the company a two-time Super Bowl winner wants to keep.
The most concerning part about Manning's 2013 performance is that he didn't finish higher on the inconsistency list. He managed just five performances above 50 and never topped 67.2 QBR.
But Manning was consistently below 40, with seven such performances, and the Giants went just 1-6 in those games.
Twice Manning dropped below the 10-point mark, against the Carolina Panthers and Seahawks.
Total QBR: 46.7
Average Variance: +/- 19.25
If Baltimore Ravens fans are looking for someone to blame for the team missing the playoffs, they can look no further than Joe Flacco.
Due to a well-balanced team, the Ravens didn't need Flacco to be great to win. When he posted a QBR of 40 or above, the team went 8-2. That includes a 4-1 record when his QBR fell between 40 and 60.
However, Flacco's QBR dropped below 40 in six games, and all six performances results in Ravens losses.
Total QBR: 61.1
Average Variance: +/- 19.53
Tom Brady obviously performed better than many of the quarterbacks ranked ahead of him on this list, but he was far from flawless in 2013.
Brady's QBR dropped below 50 just five times, but four of those performances were below 30.
And while Brady is still capable of carrying his team to victory, as he demonstrated with two QBR performances above 90, he's also capable of dragging the team down, which he showed with two scores below 20.
While Brady still ranks among the top quarterbacks in the game, his inconsistency shows that he may be nearing the end of his greatness.
Total QBR: 52.5
Average Variance: +/- 20.14
Matthew Stafford was all over the place in 2013.
At one point, he put together three consecutive performances with a QBR over 75 in Weeks 6, 7 and 8. However, he also closed the season with four straight weeks under 28.
While Stafford posted a fair number of solid outings, with six games over 70, he never turned in an elite performance to really get Detroit Lions fans' hopes up. Stafford peaked in Week 9 against the Cincinnati Bengals with a QBR of 81.9.
Total QBR: 40.1
Average Variance: +/- 20.37
Robert Griffin III's 2013 performance was obviously disappointing, but a closer look at his QBR shows it may have been even worse than some imagined.
One would expect some inconsistency from a second-year quarterback, so Griffin's placement on this list isn't shocking. However, his inconsistency wasn't a result of a wide range of good and bad performances.
Griffin topped the 50-point mark—which represents the perfectly average performance—just three times in 2013, the same number of times he dropped below the 10-point mark.
A new coaching staff and improved supporting cast may help, but there are certainly reasons to be worried about RG3.
Total QBR: 70.5
Average Variance: +/- 20.62
The Saints owe their 11 wins to Drew Brees. But, due to his relative inconsistency this year, they can blame at least four of their losses on him as well.
The Saints went 11-1 when Brees' QBR topped 50, but he mixed in a few rough outings this year.
Brees' QBR fell below 40 on four occasions this season, and it's tough to win with that type of performance from your quarterback. Not surprisingly, the Saints went 0-4 in those games.
Perhaps most concerning for the Saints heading into this weekend is the fact that Brees' worst outing, a 22.7 QBR, came in Week 13 at Seattle.
Total QBR: 66.4
Average Variance: +/- 21.35
Jay Cutler's place on this list should come as no surprise to anyone who has followed his career.
While the overall numbers are always respectable, Cutler mixes in a few duds throughout the season, which always frustrates the fans.
This year was no different, as half of Cutler's 10 starts topped 80 in QBR. However, three of his 10 starts dipped below 50, including a season-low 15.4 in Week 16 against the Philadelphia Eagles.
Total QBR: 45.6
Average Variance: +/- 21.63
A little inconsistency is expected of a rookie, so Mike Glennon's placement on this list really shouldn't be seen as a negative.
While Glennon's QBR stats were scattered, he managed to top the 50-point mark in seven of his 13 games.
An even more encouraging sign is the fact that Glennon stepped up on some of the biggest stages. Two of his four best QBR marks came on the road against the Saints and Seahawks.
Total QBR: 49.4
Average Variance: +/- 22.32
Alex Smith's QBR of 49.4 makes him nearly perfectly average, which isn't necessarily a bad quality for the game manager he has become for the Kansas City Chiefs.
Unfortunately, on a week-to-week basis, the Chiefs have no idea what they're going to get from Smith.
Despite a QBR hovering around 50, Smith only had one game in which his QBR fell between 40 and 60. In other words, he played either well enough to carry his team or poorly enough to potentially cost it the game.
Luckily for the Chiefs, of his seven games that fell below the 40-point mark, four came against the Cleveland Browns, Bills, Titans and Oakland Raiders, and the Chiefs were able to pull out close wins despite Smith's efforts.
Total QBR: 54.3
Average Variance: +/- 22.69
Ben Roethlisberger was all over the place in 2013. He carried the Pittsburgh Steelers to victory over the Bengals in Week 15 with a 90.1 QBR, but also imploded against the Chicago Bears in Week 3 with a QBR of 16.3
Overall, Roethlisberger managed to have eight games with a QBR above 50 and another eight below the mark.
It's not hard to see how Big Ben may have cost the Steelers a shot at the playoffs, as the team went 2-6 when his QBR dipped below 50, with their only victories coming against the Browns and Bills.
Total QBR: 42.3
Average Variance: +/- 22.83
Like Glennon, EJ Manuel's performance can't be viewed as all bad, considering the fact that rookies are expected to be inconsistent.
And in Manuel's case, his low QBR and his consistency may be unfairly skewed due to two dreadful performances.
Six of Manuel's 10 starts resulted in a QBR above 50 and only two dipped below 30. Unfortunately, those two outliers were a 9.8 performance against the Ravens and a 3.8 against the Tampa Bay Buccaneers.
Manuel failed to post a QBR above 80, so he never really showed any signs of greatness, but Bills fans should be at least slightly encouraged by his overall performance.
Total QBR: 69.0
Average Variance: +/- 24.15
Nick Foles gave the Eagles plenty of reasons to be encouraged about his future, but his 2013 campaign was hardly the record-setting performance that his standard quarterback rating would lead you to believe.
Foles was lights-out in three games that topped the 90-point marker, but he also was a liability in a Week 7 loss to the Cowboys when he posted a QBR of 7.5.
Total QBR: 58.9
Average Variance: +/- 24.73
Some fans have been quick to anoint Russell Wilson the next elite quarterback, but that may be a little premature.
Yes, Wilson topped 90 in Total QBR four times, but three of those four performances came against the Falcons, Vikings and Jacksonville Jaguars defenses.
On the flip side, Wilson also had five games in which his QBR dropped below 30.
Obviously, Wilson has elite tools, but consistency is not his strong suit just yet.
Total QBR: 68.6
Average Variance: +/- 25.32
Only four quarterbacks on this list topped Colin Kaepernick in Total QBR this season, but he fell flat on his face against the majority of the 49ers' toughest opponents.
As Alok Pattani of ESPN Stats & Info pointed out, Kaepernick's QBR may be inflated due to the fact that he feasted upon weak competition.
Kaepernick's QBR topped 90 four times, but it came against the Titans, Jaguars, Buccaneers and Washington Redskins.
Against defenses ranked in the top 16, however, Kaepernick managed an average QBR of just 31.2.
Total QBR: 55.8
Average Variance: +/- 25.48
Bengals fans won't be at all surprised by Andy Dalton's placement on this list.
While he's shown flashes of ability throughout his three years, you just never know which Dalton will show up on any given Sunday.
Prime example of Dalton's inconsistency: In Weeks 7 and 8, Dalton's QBR topped 90. But in the three weeks following, he managed QBRs of 13.5, 17.3 and 3.7.
Dalton's struggles have likely landed him on the hot seat entering 2014.
Total QBR: 56.2
Average Variance: +/- 26.38
While Newton dominated his weakest opponents, in nine games against defenses ranked in the top 16, Newton managed a QBR of just 39.4.
Among Newton's worst outings was his 19.2 QBR against San Francisco, which doesn't bode well for the Panthers' playoff hopes this weekend.
Total QBR: 51.9
Average Variance: +/- 28.64
Carson Palmer's QBR of 51.9 doesn't even begin to describe his performance. Palmer's QBR only fell within 20 points of his season average twice.
While Palmer's QBR did top 80 points in four games, all Arizona Cardinals wins, his QBR also fell below 30 six times.
If Palmer had been even slightly more consistent, the Cardinals would have cruised into the playoffs. In the 10 games in which Palmer top 30 in QBR, Arizona went 8-2.
Total QBR: 35.9
Average Variance: +/- 30.41
Some inconsistency is expected of all rookies, but Geno Smith's was off the charts.
While his four games above 80 certainly provide some hope, especially his QBR of 90.7 in the season finale, Smith's five games with a QBR below 10 raise far more concern.
Had Smith even played a mediocre level of football, the New York Jets likely would have been playoff-bound, but in five games (against the Titans, Bills, Ravens, Steelers and Bengals), Smith gave his team virtually no chance of being competitive. As a result, in those five contests, New York was outscored 162 to 45.
Given the strength of the Jets defense, Smith may get bumped in favor of a more consistent veteran quarterback in 2014.