Okay - I'm a stats junkie. And as you know, QBR is my preferred measure of statistical performance for quarterbacks. It takes the expected points performance of a quarterback and adjusts it for the in-game situation. it is lovely.
The only real knock on QBR is that it does not take into account the strength of the opponent. This has led to a lot of Hawks fans squawking about tough opponents for Russell Wilson Fortunately, I've done so here.
To begin, ESPN does not produce defensive adjustments for QBR in the NFL - they do at the college level, but not pros. So, I needed a surrogate. Pro-Football-Reference has found that adjusted net yards per pass attempt is an excellent surrogate for QBR -- it doesn't take into account QB rushing allowed, but it does everything else. So, I decided to use ANY/A as the surrogate. Next, I adjusted Total EPA/play (which is what QBR is) for ANY/A by dividing the league average defensive ANY/A by that specific opponent's ANY/A. Finally, I converted these scores back into QBR using the NORM.DIST function in Excel.
The results are shocking. Below is a two-game moving average of the defense-adjusted QBR for Wilson and Kaepernick:
What you see is that since Kaepernick's epic fail vs CAR in Week 10, he's been phenomenal. Wilson, on the other hand, has been on a clear pattern of decline since his bye week and he NOR game.
ESPN does the casual fan a disservice by converting z-scores (standard deviations) into percentiles. As a result, fans don't really comprehend how much better 99.9 is than 99.0. Well, I've converted them back to z-scores. 0 is league-wide 2013 average. These scores vary a bit from ESPN because their population set is 2006-2013.
As you can see, Kaepernick had a couple two standard deviation+ games against Tennessee and Jacksonville, followed by one of the worst games in the NFL in the past few seasons vs. Carolina. But since then, every game has been above average. In fact, the @NO game was darn-near the mean, and the games after @NO average about 1 standard deviations above mean.
Wilson, on the other hand, has been a below average quarterback since Thanksgiving. and if you look at his games after the @NO matchup, he's been significantly below average.
Conclusion: this is probably good evidence that Wilson has been figured out and Kaepernick has recovered from an abysmal performance against Carolina in Week 10.