Based on this tweet, I looked into Miguel Tejada's O-Swing data. I noticed an interesting trend: from 2002-2010, his O-Swing% gradually increased. I wondered if this was a league-wide trend...
So, I did a little research...I took a small sample size of 35 players who accumulated 5000+ PA from 2002-2010 (there were 42 in total...but I got sick and tired of doing the tedious work, plotting all of this data; I know, I'm lazy). I then plotted their O-Swing by age in a spreadsheet. I defined age by whatever their age was on April 1 of the respective season. I discounted seasons in which players accumulated fewer than 400 PA....
Anyway, I noticed that, typically, there is a trend existing in O-Swing%. Players have their lowest O-Swing at around age 27-29, although some were as early as 20-25.
It's tough to get a full idea of the trend, as there's only data available from 2002-2010...so a player's full career isn't mapped out. Thus, we have small glimpses. Players from 28-35, from 20-27, etc.
I have the spreadsheet, and I'll be happy to send it to anybody that's interested. I'd love to see someone help me out with this, as I'm not graph-savvy like most of the people on BtB.
In fact, I couldn't even get the spreadsheet to graph all 35 players...it only graphed five. So this is all I have to offer...
Anyway, I'd love to see what people think of this, or to see people do their own research in this area. From my limited research, there seems to be a trend in O-Swing% by age.
Mapping an entire trend like this seems do-able. I just don't know how to do it. I'm sure it's similar to the process used to develop the WAR arcs....
UPDATE -- ADDED THIS TO THE COMMENTS, BUT I'LL POST IT AGAIN HERE.
The graph's admittedly messy, but the trend appears to be visible. Obviously, small sample size is a factor here. But still...I think it's a legitimate trend. There are some theories one could infer cause this. I've already heard this idea proposed: that declining bat speed as a player ages explains the increase in O-Swing%. The theory makes sense to me...I'd love to hear what others think...