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Of Sample Sizes, Batting Averages, and the Derek Jeter

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I was re-reading an old article about sample sizes by someone much smarter than me.  And I was thinking.

Here's what we know:

A season worth of OBP is a good indicator of talent because a batter controls most of the activity involved (to swing or not).

A season worth of SLG is a good indicator of talent because a batter's talent dictates the majority of the outcome (power and speed mean more Total Bases).

A season worth of BA is not a good indicator of talent because much of BA happens outside the hitter's control (is the ball caught or not).

Here's my thought: Batting average affects OBP and SLG.

From 2009 to 2010, Derek Jeter's batting average fell 64 points.  His OBP fell 66 points.  That 19% drop in BA corresponds nicely to the 20% drop in his SLG.  I'm not sure about the impact of these observations, but the symmetry is striking.

Now, I have every reason to be confident that the 2010 Derek Jeter hit .270/.340/.370 for a reason.  This was not bad luck- this was way too many groundballs and fewer line drives.  A late season session with Kevin Long gives Yankee fans hope that Jeter's early season malaise is not going to be a lifetime condition.

And in projecting Derek Jeter's future, I'm more inclined to look at his .300/.363/.408 2008 and the average of his 2009 and 2010, .301/.372/.416. Isn't it eerie how closely the numbers line up when we take the larger sample?  I suspect they're telling us something.

Jeter is in decline, make no mistake (how does a shortstop hit .337/.413/.505 with 71SB over three years and never finish higher than third in MVP voting?).  We expect his performance to decline as he gets older.  But I think 2010 was a low point lower than could have been expected, and lower than should be expected again.

*Thanks to my friends at Beyond the Boxscore for helping me straighten out some of my thinking.