I agree that being healthy has an impact in the same way that Elvis' mental health could and likely has negatively affected his last couple seasons. I don't think Korpi (or any player) went through the season with the mindset that they need to play well to get paid more. But in leagues where guaranteed pay is a thing, it definitely happens.
You can doubt it all you want, but that study literally proves that players will over perform in contract years and will likely under perform in the year or two after the contract.
I do like his idea to put incentives or qualifiers in the year or two following the deal to keep players motivated and performing at that high level
I wasn't doubting the study, I was doubting Korpi playing for a contract. He had too much on his plate just trying to get back up to speed after missing a lot of time, and recovering from his surgery.
I have seen plenty of guys have big years in their contract year. While Korpisalo had a good year, he didn't over perform.
The study has some vagueness to it. Doesn't really say what players were picked, or how they were picked. Did they just happen to pick guys at random, or did they have a plan on which type of players. Playing at least 500 minutes or 300 innings suggests there were plenty of bench players and/or not everyday players involved. Maybe if they set the criteria higher it may mean more. Like use more everyday guys, or guys that have some star power. For example, they can take a guy like Manny Ramirez who had a nice contract year with the Indians. He hit 38 HR's and knocked in 122 in 118 games. Going to Boston the next 2 years his production in those two categories dropped per game, 41/125/142, 33/107/120. He fit the model of the study exactly, but I don't think anyone in Boston cared, as his numbers were still very good. The study may have proved what they wanted it to, but depending on the situation, sometimes it doesn't mean anything.