This is a quick little follow-up to this morning's look at positional adjustments.
So far the most common response has been, can't we have a graph baselined to the league RPA? And my counter-response – sure you can!
Even better, this one is also a link to a bigger version of the graph, so you can see things more clearly. If you'd like, you can also play with the data in a table.
Something from the discussion in the comments I want to further tease out. Justin Inaz of Beyond the Boxscore asks if there isn't a problem with assuming all positions are equal. He's certainly right that is a problem, but it turns out that's not what we're doing. For instance, if you take the average center fielder from 1955 (without correcting for skew, as I have) in a full season, in this system he'll probably be +5, assuming neutral defense. A left fielder is going to be more like a -2. So you aren't forcing everything to zero – center fielders as a group were more valuable than left fielders that year, and you're capturing that difference. I think it's important for us to note that while over long periods of time there will (probably) be equilibrium between the positions, over the short run (and by the short run I mean as much as a decade or more, like the center fielders in the 50s) anything can happen.
And that's why, after having made my adjustments as best I can, I'm living with some things that seem wonky. You've got a little three year dip or so in the third basemen in the early 90s, where they are just a shade below second basemen. Is that a data artifact? Or was that a dry spell for third basemen, which teams corrected over time? Remember that baseball players aren't totally fungible – sometimes you end up with one team having a surplus at one position, and another team having a deficiency, and so some players end up playing not the position they're best suited to, but the position their team has the greatest need at. I don't want to practice Jack Bauer sabermetrics – it turns out that data sets are like criminal suspects; under duress you can make them say anything you want. So you read the data its Miranda rights and go from there.
Which brings up a point from one of the comments over at Tom Tango's blog – jar75 notes that "(t)here has been a bit of a shift in this area though as teams have started to play guys who can cover a lot of ground in LF: Carl Crawford, Brett Gardner, Juan Pierre, Jose Tabata, Nyjer Morgan (as a Pirate), et alii." And you can actually see that reflected in the graph there – left field has dipped a bit while right field has stayed mostly flat. Historically, we've seen on major switch between RF and LF on the defensive spectrum already. Are we in the midst of another one, or is this just a short "blip?" I think it'll be a few years before we find out for sure, but I find it an interesting question.