EWSL 2011 Age and Rookie Baselines

Here’s the other necessary preliminary before launching my division previews powered by Established Win Shares Levels (originally explained here): before we get to rolling out the 2011 EWSLs, I have to update the age adjustments and rookie values I use each year. These are based on the data I have gathered over the past seven seasons, and so with each passing year, one would hope they become progressively more stable and useful in evaluating the established talent base on hand for each team entering each season. As a reminder: EWSL is not a prediction system. It’s a way of assessing the resources on hand.
I’ll skip some more of the usual preliminaries (see last year’s post) and get right to the charts:
Non-Pitchers 2010 and 2004-2010:

Pitchers 2010 and 2004-2010:

A couple of the older-age cohorts did well, which of course is partly attributable to small sample sizes – the 33-year-old hitters had a great year, led by Aubrey Huff, Alex Gonzalez and Mark Ellis as well as better bounce-backs than projected from Travis Hafner, Troy Glaus and AJ Pierzynski. The 34-year-old pitchers were bouyed by Tim Hudson and Carl Pavano, the 35-year-olds by Hiroki Kuroda, Koji Uehara, Livan Hernandez (whose actual age remains indeterminate) and the healthy-again Chris Carpenter, and the 38 year old pitchers were carried single-handedly by Billy Wagner.
On the other hand, it was a brutally tough year for some of the age brackets here, especially the 35-and-over hitters. And as you can see, not every age cohort is uniform – the 35 year old hitters were a fairly weak group, compared to the star-studded 36-year-olds, but both lost a whole bunch of value.
The real patterns can be found in the multi-year results. What has interested me the past few years is whether there is an actual change in aging patterns since baseball started cracking down on steroids – suspensions (full list here) began in 2005 and enforcement began in earnest in 2006, but I didn’t start noticing a change in the trends until after the 2008 season. So I gathered the 2004-07 results against the 2008-10 results…the comparison was somewhat inconclusive on its face, so I won’t bother you with the numbers, but I noticed something that is – on reflection – not that surprising: when comparing the 2004-07 sample to the 2008-10 sample, the proportionally smaller (per-year) group tended to do better. In other words, for example, the 30-year-old hiters held 86.2% of their value in 2004-07 compared to 95.9% in 2008-10, but 30-year-olds made up 9.58% of the hitters in the earlier group and 7.53% in the later group.
When I backed the numbers out, I noticed that (excluding rookies), 23-28 year olds made up 36.88% of the hitters in my preseason depth charts in 2004-07, compared to 42.92% in 2008-10, while the proportion of 35-and-up hitters dropped off from 16.47% to 12.9%. Among the pitchers, the proportion of pitchers age 27 and under rose from 34.97% to 40.46% over the same period, while pitchers age 34 and up dropped from 19.59% to 16.46%. Put simply, as we move away from the steroid age, fewer older players are hanging on at the margins. The results are not so dramatic as to compel me to draw a conclusion, but they certainly suggest that if we’re looking for a shift in aging patterns, it may crop up less in the arc of player performance than in what we don’t see – more guys losing jobs or hanging it up, perhaps due to injury, who might have found ways before to prolong their productive years.
Anyway, we wrap up with the rookie adjustments, which don’t really require much comment:
Rookies