One of the more interesting questions for next year's Astros is whether Miguel Tejada's offense will rebound. Last season Tejada's OPS dropped from .799 in 2007 to .729. That was a precipitous decline which was 60 to 80 points lower than what most projection systems forecasted for Tejada in 2008.
At age 34, any number of scenarios may be occurring. The worst case would be if this represents a consistent collapse with the rate of decline continuing in the coming years. Another possibility: frequently, players in their early to mid-30's will undergo a decline which is not consistent, but may mix a secondary career peak among down seasons. Some rare players, like Jeff Kent, decline so slowly that they continue to post relatively consistent superior stats.
CHONE projects cumulative probabilities for Miguel Tejada's 2009 offense. The expected value (i.e., 50% cumulative probability) is an OPS of .778. The OPS increase of 49 points over last year would be welcome. In fact, Tejada's overall batting line in 2008 is very similar to the 30% probability level in the CHONE projections, confirming the view that last year was perhaps an aberrant decline. What kind of upside is shown by CHONE? The 60th percentile is just about a .800 OPS. The 80th and 90th percentile are .in the .850 - .875 OPS range.
My next thought is to examine the age 34 and 35 seasons for some players similar to Tejada.
This isn't really scientific. But reviewing how similar players responded in their ages 34 and 35 years may suggest some possibilities for Tejada's next season.
I started with Baseball-Reference.com's comparable players to Tejada at age 34. I culled the list down to infielders, since Tejada draws several catchers as comparable offensive players. The B-Ref players: Verne Stephens, Jeff Kent, Ken Boyer, Joe Torre, and Ryne Sandberg. Because the list has only one shortstop and three middle infielders, I also added the following players: Barry Larkin, Allen Trammell, and Lou Whitaker. Given the different eras for these players, I will use OPS+ for the comparison. An OPS+ of 100 is an adjusted version of league average. Tejada posted an OPS+ of 92 in 2008.
Below, for each player, I show the OPS+ for ages 34 and 35, respectively, followed by a "peak percentage," which is the player's highest OPS+ at ages 34-35 divided by the player's career peak OPS+. Because Stephens did not have a age 35 season, I used age 33 and 34 for him. I used ages 34 and 36 for Sandburg, because he retired in disgust after his age 34 season, but un-retired to rebound at age 36.
Kent 147, 119 90%
Stephens 101, 102 62%
Boyer 90, 101 63%
Torre 91, 123 71%
Sandberg 83, 96 69%
Larkin 134, 104 69%
Whitaker 141, 136 100%
Trammell 114, 138 74%
Tejada 92, ?, ?
Miguel Tejada's 2008 season was 70% of his peak season. Certainly the examples above show that other premier infielders have been very productive at age 35, but the results aren't conclusive. The average "percent peak" at age 34/35 for the comparable players above is 77%. If Tejada has a 77% percent peak in 2009, he will post a 101 OPS+. The league average park adjusted OPS, based on the last three seasons, is .766. The .776 OPS projected by CHONE for Tejada is 101% of .766.
The CHONE projection is reasonably similar to other 09 projections for Tejada. Bill James and ZIPS both forecast a slightly more optimistic .785 OPS for Tejada.
I haven't factored in any impact of Tejada's legal problems. That is so speculative that it is impossible to forecast the impact in an objective way.
What kind of performance do you expect from Tejada next year?