The PECOTA system is a conservative one. Its player-performance projections are neither wildly optimistic nor pessimistic but built purely from the data and from its understanding of the way player careers progress based on literally thousands of antecedents. Thus, when PECOTA proposed that Orioles catching prospect Matt Wieters, a rookie-to-be who has never played above Double-A, could hit .311 with a .395 on-base percentage and a .544 slugging percentage in the majors this season, we took notice -- this was the first time PECOTA had looked at a prospect and predicted an MVP-caliber, Hall of Fame-level season right off the bat.
By way of comparison, consider the two players who won the 2008 rookie of the year awards in their respective leagues, both of whom PECOTA liked from the get-go. Tampa Bay Rays third baseman Evan Longoria received a weighted mean projection of .266/.339/.459. This was no surprise; by acclamation, Longoria was one of the most talented young players in the game. However, PECOTA goes only by what it sees in the player's profile, both in terms of performance and vital statistics, so although it was quite high on Longoria compared to most other prospects, it did not overestimate him. In fact, PECOTA proved to be a little too reserved in this instance, as Longoria hit .272/.343/.531 -- the projection nailing the batting average and on-base components of Longoria's rookie year, but missing low on his power.