Here are the final numbers for quarterback Win Probability Added (WPA) and Expected Points Added (EPA) for the 2009 season. These numbers include playoff performance. I've posted these stats previously for selected players, but this is the first time I've published a comprehensive list. This is the first time I've truly had confidence in the absolute values of the WPA stats. Previously, they really could only be relied on for relative comparisons between players.
You might notice that the WPA and EPA stat totals vary from the previous posts. That's because I've fixed some discrepancies in both systems. For the WP model, I've recalibrated the parameters so that the grand sum of all plays in all seasons add up to zero. Previously, there was a tiny positive bias on every play that when added up over hundreds of plays made a significant difference. Additionally, the EPA model now excludes final plays of each half. Previously, EPA counted the final play of each half as a very negative event. EPA calculates the difference between the net point value before the play and the net point value after the play. Because the EP value at the end of a half is always zero, my system was heavily penalizing players who participated in the these plays. This affected QBs in particular because many final plays are kneel-downs. There are still some tweaks and fixes to be made, but they are relatively minor.
One other thing to note up front is that the payoff for passing is predominantly better than for running in terms of both WPA and EPA. I've published extensively on the apparent advantage of passing over running based on the EPA model, but I have yet to publish any research based on the WP model. Now that it's been calibrated properly, we have a way to discern the relative value of passing vs. running while taking into account the considerations of time and score. Much of the value of running is obviously when a team with the lead can burn time off the clock, but that's a discussion for another article. The bottom line here is that the average QB will have significantly positive WPA and EPA totals. (Conversely, the average running back will have a negative totals.)
The first table below lists the top QBs, plus some other notable ones, ranked according to their 2009 WPA totals. Total EPA is also listed for each QB. The last column, Ratio, is something new. It's simply the ratio of a QB's WPA to his EPA. This is a rough measure of leverage, timing, or "clutchness." In other words, it measures how much win probability a QB squeezed out of his raw performance due to situational factors.
Teams with QBs who had a very high WPA/EPA ratio could be expected to regress next season. EPA is less context-dependent and therefore can be expected to be more repeatable. Guys like Shaun Hill, Bruce Gradkowski, and Mark Sanchez did more with less in 2009, but we shouldn't count on them to do the same in 2010. Trent Edwards has a very high ratio, but that can be discounted due to a very tiny EPA. (Someone with a perfectly-average zero EPA would have an infinite ratio.) I may need to come up with a more robust way to calculate this--suggestions are welcome.
Click on the headers to sort.
The second table lists each QB's WPA and EPA on a per-play basis.