baseball player movement historical trends

Question
Is it really true that, as some claim, baseball players change teams more frequently now than in past eras?  I see you wrote an article on this question in BRJ in 2000 and was wondering what results you found.  

Answer
Perry,

I believe I did a pretty decent study on the player switching matter.  I used an available baseball database (Sean Lahman's statistical information) and parsed it out determining every team switch every player in baseball history made.  I divided players into four groups (19th century, Golden Age (1901-1960), expansion (1961-74), and free agency (1975-99).  I also looked at player by career length.

Some of the conclusions:

- 19th century players switched way more often then any other era (which is expected because of the great instability of baseball at the time).  The average 19th century player switched teams every 2.4 years (and they had the shortest career length (3.5 years) so you really couldn't tell the players without a scorecard (but since they didn't wear numbers, you had no idea who was out there!)
- Every other category player averaged 3.8 years playing career per team switch
- Golden age stars did switch teams slightly less frequently, but since their careers were shorter, roster turnover was still higher then today.
- Stars (10+ year careers) switch teams 5% frequently then the average major leaguer
- One team stars have always been rare, but the number is trending down.  19th century, 1.4%; golden age, 8.2%; expansion, 7.3%; and free agency, 6.2%.  The percentages are number of one team stars divided by total number of stars.

But it does seem that players are switching teams even more frequently in the last five years since the study was done.  A restudy might find these numbers dropping a little more.  But one interesting thing.  Players are less likely to have a short career (one year) then ever.  Once you become a major leaguer, it seems a team is more likely to employ you then try and find a new player out there.  So the total population of major leaguers is probably more stable now then at any other time in baseball history.  Interesting - maybe I'll have to look at that.

Hope this helps!

Brian