Sunday, February 19, 2012
Park factor fix for Forecasts
Posted by Brian CartwrightThe Forecasts update posted yesterday, Feb. 18, will have different numbers for every player from the week before, as I discovered a logic error in my code which was preventing park factors from being applied to each player's batting and pitching projections. Recently published Forecasts were park neutral but now are as intended, specific to the player's team.
Major league players' projections are customized to the weighted mean of all the ballparks his team played in the previous season. Projections for players in the minor leagues are based on their parent major league team. Schedules for 2012 may now be downloaded from mlb.com, and as soon as those are imported into the Oliver database, I will use the number of games scheduled to be played in each ballpark in the coming season instead of the previous.
I do not expect using 2012 instead of 2011 to produce major changes in the projections, but some players who play in extreme parks did see sizable differences when their park factors were correctly applied. Troy Tulowitzki solidified his rank as the overall best position player; playing half his games in Coors Field inflates his batting projection from a park neutral .285/.358/.506 to .302/.371/.544. On the other end of the ballpark spectrum, half a season in Petco Park (as well as a disproportionate number in parks such as Dodger Stadium and AT&T Park) drop Chase Headley's projection from .283/.353/.408 to .269/.342/.383.
I apologize for any inconvenience and welcome any comments from subscribers who suspect something may be amiss. Sometimes we'll have an explanation, but other times we have been able to catch errors. As a result of Matt Swartz's testing at FanGraphs of several projections, including Oliver, I am currently at work on some improvements on projecting ERA, as well as an existing project to be able to project a pitcher as either a starter or a reliever for those times when a player's role changes.
Brian got his start in amateur baseball way back in the 1970's as the statistician for his local college summer league in Johnstown, Pa, which also hosts the annual All-American Amateur Baseball Association. A longtime APBA and Strat-o-Matic player, he still tends to look at everything as a simulation. He has also written for StatSpeak and Fangraphs, was runnerup in the Baseball Prospectus Idol competition, and has consulted for a major league team. You can contact him at .(JavaScript must be enabled to view this email address).
Can you explain what process you use to project park factors for the upcoming season? Thanks.