About a year ago, I published an article on my PrOPS system in The Hardball Times Baseball Annual 2006. While the article did get some positive media attention (here, here), I occasionally run across skeptical comments from baseball fans. Some people feel the system hasn’t been tested, but that’s incorrect. The fact is, the PrOPS formula is derived from observed correlations in past data. And I reported the results of how well the formula captures over/under performance in the article.
There is a highly statistically significant relationship…between a player’s over/under performance and his decline/improvement. And the greater the the deviation between PrOPS and OPS, the larger the reversion is the following season. For every 0.01 increase/decrease in a player’s over/under performance, his OPS is likely to fall/rise by 0.008 the following season. For example, a player with an OPS 10 “points” above his PrOPS, can expect his OPS to fall by eight points in the following season. That is quite a reversion.
I also generated lists of the top-25 over and under performing season from 2002-2004. And what happened to them?
Of the top 25 over performers, 20 players had lower OPS in the following season.
Of the top 25 under performers, 21 improved their OPS in the following season.
The article also lists the top-25 over and under performers for 2005. What happened to those players in 2006?
Of the over performers, 12 players declined, 7 improved, and 6 did not deviate more than 20 OPS-points from the previous season. Of the under performers, 11 players improved, 7 declined, 3 had no change, and 5 didn’t garner serious playing time. It’s not an air-tight projection system, but there seems to be some information there.
PrOPS is not a stand-alone projection tool. You should not look only at a player’s PrOPS and assume it’s exactly what the player should be doing. When I look at it, I also consider the player’s recent hitting history, injuries, aging, and all that other stuff we sometimes use to evaluate hitters. But when I see a player have a career year, and his PrOPS don’t show it, I start to get suspicious.
If you’re curious about the over/under performers of 2006, see The Hardball Times.