It has been one year since I first wrote about quarterback salaries at Football Outsiders; here's a link to last year's article in which I first compared quarterbacks' statistical performances to their salaries. A quick reminder: quarterbacks were measured by their TANY/A (Total Adjusted Net Yards/Attempt, including passing, rushing, and sack data) and PAYD (Pay by Average Yards and Demand, which accounts for both quality and volume of a quarterback's plays).
This year, in the ongoing task of determining how much a quarterback is actually worth, I'll be going over a new modifier to PAYD determination.