Long-term league quality indicators

First, credit where credit is due

I don't want anyone to get the idea that using error rates to assess league quality is a new idea. In fact, Bill James himself identified fielding percentage as an indicator of league quality. The error rate and the fielding percentage are just two ways of looking at the same information.


Historical charts of major league stats are available at A Graphical History of Baseball (hat tip: Baseball Musings).

Here's the chart of Errors Per Game (per team):


By this standard alone, the IBL would match the early 1900's with 2.2 errors per nine innings. (If it's any consolation, some of the 2007 rookie leagues are in the same zone.)

Stolen base rates, however, do not track the long-term improvements in league quality. Steals fell to their lowest levels around 1950, then rose until the 1980s, and have declined since then:



I don't know what changes in the game gave rise to these trends in the steal rate - perhaps shifts in runner skill versus pitcher skill? Or maybe it was all Rickey Henderson's fault!

(Update: Duh! Of course, a major factor in the number of steals per game is the overall level of offense - the more baserunners, the more steal opportunities. That's why the relevant steal rate is steals per runner on base, not steals per game.)

It certainly remains possible that the steal rate correlates with league quality at any particular point in time, as my earlier graphs seem to demonstrate. But the steal rate would seem to be a far less reliable gauge of league quality than the error rate, so I'm less inclined to downgrade my assessment of the IBL's quality on the sole basis of its high steal rate. (The IBL's steal rate was 2.5 per nine innings, nearly double the MLB's record levels from the early 1900s!)