From Bill James' 2005 SABR article, "Underestimating the Fog":
If this was a real scientific journal and I was a real academic, the title of this article would be The Problem of Distinguishing Between Transient and Persistent Phenomena When Dealing with Variables from a Statistically Unstable Platform. But I was hoping somebody might actually read it.
I have come to realize, over the last three years, that a wide range of conclusions in sabermetrics may be unfounded, due to the reliance on a commonly accepted method which seems, intuitively, that it ought to work, but which in practice may not actually work at all. The problem has to do with distinguishing between transient and persistent phenomena, so let me start there.
If you make up a list of the leading hitters in the National League in 1982 (or any other year) and check their batting averages in 1983 (or the follow-up year, whatever it is) you will quite certainly find that those hitters hit far better than average in the follow-up season. If you look at the stolen base leaders in the National League in 1982, you will find that those players continued to steal bases in 1983. If you look at the Hit By Pitch Leaders in 1982, you will find that those players continued to be hit by pitches in 1983. That is what we mean by a persistent phenomenon—that the people who are good at it one year are good at it the next year as well.
If the opposite is true—if the people who do well in a category
one year do not tend to do well in the same category the next year—that’s what we mean by a transient phenomenon. Here today, gone tomorrow.
All “real” skills in baseball (or anything else) are persistent at least to some extent. Intelligence, bicycle riding, alcoholism, income-earning capacity, height, weight, cleanliness, greed, bad breath, the ownership of dogs or llamas and the tendency to vote Republican . . . all of these are persistent phenomena.
Everything real is persistent to some measurable extent. Therefore, if something cannot be measured as persistent, we tend to assume that it is not real.
There are, in sabermetrics, a very wide range of things which have been labeled as “not real” or “not of any significance”because they cannot be measured as having any persistence.
Tags: Bill James, baseball, Moneyball