Thursday, March 6, 2014

MLB Batter Consistency

In chapter 9 of our book, The Wages of Wins, we talk about player consistency and find that some sports players are more consistent and some sports players are less consistent.  For MLB we found that batter are more consistent than NFL QB's and less consistent than NBA players.  Here what I want to do is update the book for MLB batters.  So I am taking the 2000 - 2012 seasons (actually the pair of MLB seasons from 1999-2000 to 2012-2013 and looking at how consistent MLB batters are over this time period.

First let me start by acknowledging that I used Sean Lahman's MLB database to do this analysis.  Second, I restricted the MLB batters to only those who had 100 AB's (at bats) in an individual season and then looked at whether players had two consecuative seasons in which they had 100 AB's.  If this requirement is met, then they are being evaluated.  We decided to restrict the number of AB's given that some very good players may have been injured for a substantial portion of the season or that some players may have been called up at the end of one season and given a full time roll in the next season.  In both cases these players would be judged inconsistent, but not because of their play but rather due to circumstances beyond their control.

Given the AB restriction, I ended up with 4694 players who had back-to-back seasons of at least 100 AB's from the 1999-2000 to 2012-2013 seasons.

MLB batter consistency is measured by where they rank in terms of runs created in a given season.  For simplicity in The Wages of Wins, we took a player who was in the top 20% of the league in runs created as having a rank equal to 1, the next highest 20% with a rank of 2, all the way to the lowest 20% with a rank of 5.  If a player maintains their rank from one season to another they are considered to be consistent and if not, they are considered to be inconsistent.  (As you will see I also looked at players who only moved up or down one rank from one season to the next).

So how consistent are MLB players over this time period?  I find that 38% (1774 observations) of MLB batters consistently perform as measured by runs created from one season to the next.  Additionally, 39% (1827 observations) move either up or down one rank from one season to the next, meaning that during the 1999/00 to 2012/13 MLB seasons 24% (1093 observations) of MLB batters with back-to-back seasons of 100 AB's moved up or down two or more ranks from one season to another.  Compared to NHL goalies, MLB batters are more consistent.

Of those who were consistent from one season to another, that could mean they were in the top 20% or could be in the bottom 20%.  So what is the distribution of consistently "good" MLB batters as opposed to consistently "bad" MLB batters.  Of the 1774 observations of MLB batters that keep their same rank from one season to the next, 697 (or 39%) of those MLB batters were in the top 20% of MLB batters and only 208 (or almost 12%) were in the bottom 20% of MLB batters.

The next blog will be a guide to calculate player consistency using the 20% dividing line.

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