From Bill James' 2005 SABR article, "Underestimating the Fog":
I believe that a more careful study, steering clear of comparison offshoots, is still likely to demonstrate that hitters perform (essentially) independent of one another, except in a few isolated cases.
In a sense, it is like this: a sentry is looking through a fog, trying to see if there is an invading army out there, somewhere through the fog. He looks for a long time, and he can’t see any invaders, so he goes and gets a really, really bright light to shine into the fog. Still doesn’t see anything.
The sentry returns and reports that there is just no army out there—but the problem is, he has underestimated the density of the fog. It seems, intuitively, that if you shine a bright enough light into the fog, if there was an army out there you’d have to be able to see it—but in fact you can’t. That’s where we are: we’re trying to see if there’s an army out there, and we have confident reports that the coast is clear—but we may have underestimated the density of the fog. The randomness of the data is the fog. What I am saying in this article is that the fog may be many times more dense than we have been allowing for. Let’s look again; let’s give the fog a little more credit. Let’s not be too sure that we haven’t been missing something important.
Tags: Bill James, baseball, Moneyball