I'm sure that recently crowned MVPs Albert Pujols and Alex Rodriguez had more than their usual Thanksgiving feast last week, what with the award and a little bonus money to do some Christmas shopping with ($200K, $1 million, respectively) to be thankful for. But before they get too fat and giggly, it's never to early to ask: How are this year's Most Valuable Players -- arguably the top two players in the game -- going to fare in 2006? One can use any number of prognosticating tools, of course, but I decided to apply the "MVP effect" -- that is, what happens to MVPs in the season following their winning the award. Now of course, worthiness in winning the MVP is a subjective matter; however, what happens to the player in the subsequent season is indeed quantifiable. Whether the mantle of "Most Valuable" has anything to do with a falloff -- or upswing -- in the player's career is another matter.
To get an idea of what we can expect from Mssrs. Pujols and Rodriguez next season, I looked at the non-pitcher MVPs from both leagues since 1985 (in addition to getting a decent sample, I thought it was a fun coincidence that it was the last time both the Cardinals and Yankees were so honored). In each of the categories listed, I took the average change for each MVP and applied it to the 2005 numbers for A-Pu and A-Rod. For example, the group of recent MVPs saw a decline in their followup year in SLG, producing an average of only around 91% of their MVP season's SLG. So for Pujols, who had an impressive SLG of .609 in 2005, I project he'll drop off to a still-potent .556 in 2006. In general, reigning MVPs the last 20 years have suffered a decline their followup season in plate appearances and in most of the important batting categories, regardless of age or league.
The sample size may still be too small for a reliable projection, and since I only counted the MVP season and the lone followup year, I'm not considering career statistics. Note, however, that Barry Bonds, Juan Gonzalez, Frank Thomas and Rodriguez have won the award multiple times, and Bonds and Thomas have won back-to-back, generally after improving upon their previous MVP season. 
Now, most players would gladly take those numbers for a season -- they'd make a career year for most. For Albert and A-Rod, they'd represent a letdown. On the positive side, if someone said that the Cardinals and Yankees would get around 90% of their MVP's 2005 season next year, fans could live with it. But then again, these are just numbers, and my methodology is far from scientific. Come November 2006, we'll see if I'm onto something -- or if I'm the turkey here.
Thanks to baseball-reference.com for the statistics.