From the mist of discussions centering around the trade value of Alfonso Soriano relative to Corey Hart, I wanted to take a look at the persistance of 20/20 hitters. Soriano did not reach that milestone last season, but Hart did. Given the difference in draft rounds (Soriano ADP 14 and Hart ADP 58), I wanted to see how reasonable my assertion that Corey Hart is more valuable than Alfonzo Soriano under the expectation that Hart will continue to be a 20/20.
As I have done in previous examinations, I looked at those players who have gone 20/20 over the past three seasons and checked how they did in their following seasons. The first thing I noticed was there were more players who accomplished the feat in 2007 (12) than did in the past two seasons combined (11). I can't help but think the move away from PEDs has shifted the game from being power-focused to a more speed-focused one.
In 2006, five players went at least 20/20. The next season two did it again, and, in 2007, two of these five did it again. While I can't say that five-man sample is conclusive, I do see support that speed is consistent. Of those 10 follow-up seasons, nine had double digit steals with only Jason Bay's 4 SB one from 2007 being the expception.
The story was the same for the 2006 20/20 players. There were seven with Grady Sizemore and Alfonso Soriano carrying over from 2005. In this case, the follow-up season was 20/20 for five of the seven, and none had fewer than 18 SBs (Mike Cameron and Soriano with 19). This further strengethens my opinion that speed is durable.
If true, then I can look at the 12 players from 2007 and reasonably expect them to produce in ways that will not disappoint. Given I am trying to learn about 2008, I ran all the players in the 2005-2007 season who accomplished the feat and pulled Baseball Prospectus' 2008 PECOTA forecasts to see what to expect.
Outside of Jason Bay, SB appear likely to continue especially in light of the fact PECOTA relies on a weighted mean projection (def from BP: The Weighted Mean forecast incorporates all of the player's potential outcomes into a single average, weighted based on projected playing time.) As a result, these stats will necessarily be lower than one will see at season's end.
PECOTA appears to agree that SB are durable given all the players are expected to produce in the 20's area sans Jason Bay. More to the point, it also seems to support my contention that Corey Hart is as valuable as Alfonso Soriano. Soriano far out-RBI's Hart, but I have a hard time accepting that until I see Soriano hitting in the heart of the Cubs line-up and not from the lead-off spot where he got 542 of his 579 ABs in 2007.