How badly has Favre played?

Minnesota Vikings quarterback Brett Favre was not on the field during the early portion of practice Thursday, which was fully expected and doesn't have much bearing on whether he will start Sunday at the New England Patriots. Favre, who has two fractures in his left foot, has said the earliest he would try to practice is Friday.

This relative break in the news cycle gives us a chance to consider in further detail the darker part of this scenario. Will Favre's poor play this season factor in to coach Brad Childress' decision?

I've already suggested that the Vikings would have a hard time benching Favre outright after begging him to return and giving him a raise to at least $16 million in total compensation this season. But what about a benching masked by an injury? That might be a possibility, especially when you consider a unique and telling statistical analysis over at Brian Burke's Advanced NFL Stats.

Burke uses a metric called Win Probability Added (WPA). Essentially, it's a way to measure how a player's performance impacts his team's chances to win or lose. (Here is the complete explanation for those interested.)

We already know that Favre's 68.0 passer rating is the fourth worst among NFL quarterbacks. But the nuanced WPA paints a more dire picture. His WPA rating is by far the worst among 39 qualifiers. In fact, his standing in this metric is three times worse than the next-lowest rated quarterback.

One way of looking at this statistic is that no quarterback is hurting his team more than Favre -- not the Chicago Bears' Jay Cutler, not the Cincinnati Bengals' Carson Palmer not even Trent Edwards of Buffalo/Jacksonville. In fact, Favre is hurting his team three times as much as Cutler, who ranks one spot ahead of Favre in WPA.

Quoting Burke: "Everyone knows Favre isn't doing well, and we don't need fancy stats to tell us that. But when we actually quantify just how bad his play has been so far, it's eye-popping."

Indeed, anyone who has watched Favre commit 14 turnovers this season knows he hasn't been very good in 2010. But Burke's metric reflects the type of analysis NFL teams often make, detailing what the mistakes lead to and whether they are made up for in other situations. When your quarterback is not only struggling, but is hurting your team far more than any other quarterback in the league, would you at least consider a change?