The effects of Brett Favre's retirement

Jackson has some elusiveness, but he's no No. 4. Getty Images

The rumored decision of Brett Favre to retire sends shock waves through a Minnesota Vikings offense that was expected to be among the league's best. Thanks to Favre's arrival last year, the Vikings jumped from 18th in offensive DVOA in 2008 to seventh in '09, while scoring nearly 100 more points.

So, assuming the Vikings are unable to convince Favre to come back for one more season, how will they do without him in the lineup in 2010?

Fortunately, our KUBIAK fantasy football projection system prepares for exactly this scenario every year, using a player's previous performance (where available) and team variables to project a full-season line for backups. One such projection in 2008 was for Matt Cassel, who had thrown 39 career passes before Tom Brady went down with a torn ACL. KUBIAK suggested he'd complete 62.5 percent of his passes and throw for 3,751 yards; he completed 63.4 percent of his passes and threw for 3,693 yards.

Fortunately, with new Vikings starter Tarvaris Jackson, we have 545 pass attempts to work from in projecting his performance. KUBIAK has calculated the expected performances for both Favre and Jackson and, well, there's a pretty dramatic difference.