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What's Good? How about Great?

Publication Date: January 14, 2004

Rules of Thumb

This week I want to look at a question that was put to me a while back by Lee Bowen, Florida State's radio guy. A lot of what we in the analysis community try to do is to better our understanding of player performance by coming up with more and more exact measures of offensive performance. Now, a lot of good stuff has come out of that, and it's hard to really get a good feel for performance without understanding things like adjusting for ballpark and competition factors, but one thing that can be missing sometimes is a simple rule of thumb.

For those of us who grew up before the analysis explosion (and I fall into that category, but only because I paid attention to baseball from a fairly young age), it was simple. A .300 hitter was a good hitter. This didn't turn out to always be true, since it's possible to hit .300 in some contexts with some other factors and be fairly worthless, but for professional baseball through the 70's and 80's, it worked fairly well when watching a team you weren't all that familiar with -- "Is this guy any good?" "Well, he's hitting .308." "OK, better pay attention." In that spirit of inexactitude, then, I want to look at last year's performances and see if we can come up with some simple numbers to remember as you head to the park this week (what, you hadn't noticed that the season starts Friday out in Hilo?).

The vastly varying length of the season makes it hard to do this for counting stats, but here are the average and standard deviation for the three big hitting rate stats for all the regulars (guys with at least 160 plate appearances) I can find for 2003:

        Avg     SD

AVG    .308    .042
OBP    .387    .047
SLG    .459    .101

Now, this covers a population of 1676 hitters. Out of that crew, for each stat there were around 260 guys (about 15%) who hit the average plus one standard deviation mark, and around 45-60 (2-3%) who managed average plus two standard deviations (Rickie Weeks was an absolutely absurd four standard deviations above average in slugging, but we're trying for something repeatable here). Those strike me as reasonable markers for "good" and "great". Last year's numbers were the lowest they've been since about 1995 or so, but they weren't off-the-charts lower than the year before, and I think they make a decent predictor for the next few years.

There you have it, then. A "good" hitter will have around a .350 average, a .430 OBP, and a .560 slugging average. A "great" one will go .390/.480/.660. Variations among the three numbers will point out the player's strengths and weaknesses between contact, plate discipline and power.

On the other side of the ball, by the way, the average ERA for pitchers with at least ten starts was 4.75 with a standard deviation of 1.58. That means (well, first of all, it means 4.75 is average, so adjust that mental marker upward) that a "good" pitcher would be around 3.25 if we used the average-minus-one-standard-deviation model. ERA doesn't follow anything close to a statistically normal distribution (neither do the hitting stats, really), though, so there were only two guys who were two standard deviations below the average. I'd probably adjust that to say that 3.75 should qualify as "good", and 2.75 is a good fit for "great".

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Boyd's World-> Breadcrumbs Back to Omaha-> What's Good? How about Great? About the author, Boyd Nation