As I get into my weekly box of numbers, it occurs to me that I should tape some sort of warning label to the top, because, as we know, not all statistics are created equally. Not every number is as meaningful, or meaningful in the same manner, as its neighbors. And one that I particularly feel like appending an asterisk to — but which I nevertheless use around these parts quite frequently — is weighted Runs Created Plus, or wRC+ for short.
There are several reasons to be wary of wRC+ in the context of prospect evaluation. All statistical analysis is, ultimately, the product of somebody’s hypothesis — if I put these numbers together in such and such a way, do they reveal anything meaningful to me? And along the way in this process, that hypothesis, and those calculations, are put through rigorous testing to see if the model really does say anything meaningful. It’s compared to other stats, compared to historical trends, compared to different environments, all in an attempt to garner some slightly more precise version of the facts than what is otherwise available. Does wRC+ tell us something more about an hitter’s season than just relying on batting average or OPS? Certainly it does, making use of the entire history of major league baseball, with literally every event over a century and half’s worth of games crunched into the equation, to determine how to weight the various outcomes of an at bat — in the major leagues!
And that’s a crucial equivocation. Weighted Runs Created was not designed for — and has never been tested against — the unique set of circumstances that make up minor league baseball. It tells us something meaningful about a league that contains the best players in the world, with a pretty flat variation in competitive ability, that is mostly stable from year to year — the players who make up an MLB season don’t change much from one season to the next.
None of those things are remotely true of the minor leagues, where the turnover in players from one year to the next is immense. Even within a season the turnover is radical. You also have much wider variation in ability, with prodigies shooting upwards and through mixed with prospects who wash out or get sent down, as well as a spattering of indy ball guys signed to get through innings. And the lower down through levels you go, the more disparate the mix is. In Low A, especially in the second half, you typically get a mix of high drafted college players mixing in with a group of players who will never advanced beyond the level and some who really never deserved to be there in the first place. It’s all combustible, mercurial, and hard to get a hold on. And it is certainly not an environment on which most advanced analytical tools (publicly available ones anyway) that we associate with MLB have ever been shown to have much meaning.
So yes, I use wRC+ here — it’s an easy sort of shorthand for showing that .300/.400/.500 means very different things in the PCL than it does in the Eastern League, for instance. But I use it as just one among a number of other lenses. Even in the major leagues, wRC+ is mostly a descriptive stat not a predictive one — it says more about what has happened than what will happen. So look at it, use it, put it in your statistical toolbox — but don’t think that it is a particularly meaningful single number for evaluating player development.
And with that, the hard, cold numbers…
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