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What happens if Seahawks need backup QB

A newly re-signed Tarvaris Jackson will compete against Brady Quinn for the No. 2 job behind Seattle Seahawks starting quarterback Russell Wilson.

The way those players performed in their most recent starts suggests the team would be better off with Jackson as the starter if Wilson became unavailable.

We could make that case by noting that Jackson posted a 7-7 record with Seattle in 2011, his most recent season as a starter, while Quinn went 1-7 with Kansas City last season. But if we wanted a breakdown more specific to the quarterbacks, we could revisit a method we used when estimating NFC West quarterback values about five weeks ago.

Stats in 16 Most Recent Starts

That method suggests Wilson's performance for the full 2012 season provided about 3.8 additional victories relative to the 2011 version of Jackson and an additional 6.5 victories relative to the 2012 version of Quinn, based upon Total QBR scores for those players.

Teams posting Total QBR scores around 50 can expect to win about half the time. That baseline allows for calculating how many added victories a quarterback provides or takes away over the course of a 16-game season and relative to another player.

In the Seattle example, we start by averaging the single-game QBR scores for Wilson last season. The result was 63.9. We then average the single-game scores for the 14 games Jackson started in 2011 (40.1) and subtract the total from 63.9. The result rounds to 23.77. We then take 23.77 percent of 16 games to determine how many victories Wilson would provide over Jackson, based upon how each played in his last season as a starter.

By this measure, Wilson added 3.8 victories over what Jackson would have provided over a 16-game schedule if he had been the Seahawks' starter instead of Wilson, and had he performed the way he did in 2011. The calculation for Quinn goes like this: Wilson's average QBR score (63.9) minus Quinn's average QBR score last season (23.0875) equals 40.8125, which taken as a percentage of 16 games equals 6.53 additional victories with Wilson.

The difference between Jackson in relation to Wilson (minus 3.8 victories) and Quinn in relation to Wilson (minus-6.5 victories) works out to 2.7 victories -- say, the difference between 8-8 and 5-11 if the team played Jackson instead of Quinn over a full season.

The differences could become even more pronounced if we considered other factors. For example, Wilson had a 78.2 average QBR score over his final nine games. He might be more apt to play near that level in the future than how he played in the first seven games of his career. Also, Jackson played much of the 2011 season with a torn pectoral muscle. Taking those things into account would change the calculations.

Note that averaging the single-game QBR scores for Wilson produced a number (63.9) that is lower than his cumulative QBR score for the season (69.6, as displayed in the first chart). We would see similar disparities if we compared a basketball player's average game-by-game shooting percentages to his cumulative percentages. Making both foul shots in one game and missing all four attempts in another would produce a 50 percent average and a 33 percent rate.

The chart below shows stats for current NFC West backup quarterbacks since 2008.