Red Sox RCI (Roster Change Index)
I've come up with a rough system to try to quantify these measurements by examining historical statistics. It works like this:
For the offense, add up the total of all the plate appearances for a given season. The Red Sox had 6,476 plate appearances in 2005. Then look at how many of these plate appearances came from players that were gone by the following season. For the Sox in 2005, this was 3,826 (from Damon, Renteria, Mueller, Millar, etc.)
The idea here is to try to weight the loss of a player by his playing time - losing an everyday starter like Damon, who was up 700 times, is more significant than losing Roberto Petagine and his 36 ups.
For the pitching, perform a similar calculation, using batters faced by each pitcher. This parallels the offensive situation - you are essentially looking at how much you saw each pitcher over the course of the season. The Sox had 6,277 batters faced from their pitching staff in 2005, and of these, 2,437 were from pitchers who are now gone (mostly from Arroyo and Miller, but also Halama, Embree, and a host of others).
Totalling these numbers up, the Red Sox lost 49.3% of their 2005 players. I'm calling this value the Roster Change Index, or RCI. The Red Sox RCI of 49.3% for 2005 means that pretty close to half the players we saw in 2005 are gone in 2006. This seems high, but for historical perspective, the question to ask is how it compares to previous seasons. Using data from Retrosheet, I looked at Red Sox rosters going back to 1901 and performed this same set of calculations for each year. The results are shown below (note that you can click on the graph for a larger view).
Looking at the 2005 figure in historical perspective, we can see that it is well above the values in recent years, and in fact is the fourth-highest value in team history. The only three years that had higher levels of player change were the following:
- 1945 (RCI = 58.4%) The conclusion of WWII saw the return of many prominent players who had been serving in the military, such as Ted Williams, Dom DiMaggio, and Joe Dobson. This displaced many of the players who had been playing during the war years, and so the 1945-1946 transition was the largest change in team history.
- 1994 (RCI = 56.8%) The strike year. The strike began in August 1994, cancelled the second half of the 1994 season, the 1994 post-season, and the beginning of the 1995 season. This resulted in substantial shakeups to the lineups of many teams, and the Red Sox were no exception.
- 1922 (RCI = 50.0%) The late teens and early twenties were a period of fairly high changes from year-to-year, with 1922 being the peak. Almost the whole pitching staff turned over in 1922, including Jack Quinn and Herb Pennock.
It's also interesting to note that although the RCI has been high in recent years, the levels aren't that different from other historical periods. The first decade of the team, along with the period from the late teens through WWII, saw rosters changing roughly at the same rate that they have been over the last ten years. The biggest long-term shift appears to be right around the 1994 strike, when we went from levels of roster change averaging around 20%, up to the current levels averaging around 35%.
A couple notes on the methodology: I'm not attempting to distinguish between players lost in the offseason and players lost during the season. So Damon (traded in the offseason to the Yankees) and Bellhorn (cut in the middle of the 2005 season) essentially fall into the same category - they appeared in 2005, but are gone in 2006. This makes sense, because the question we're trying to answer here is "How different is the 2006 team from the 2005 team?". Also, the 2006 season is just getting underway, so there is still the possibility that some players who were active in 2005 might still appear in 2006. For example, if Cla Meredith, currently with the PawSox, were to be brought back up, or if Bellhorn (perish the thought) were to be reacquired, then the total change number from 2005 to 2006 would go down, because these guys are currently being counted as "appeared in 2005 and gone in 2006".