Dan Brooks talks about the human element of umpiring.

Update: Calling balls and strikes is a difficult task.

Update: What happens at the edge of the strike zone?

Update: Dan is talking about the logistic function.

Update: Umpires will call strikes well off the edge of the plate, 50% four inches off the plate.

Update: Lots of variation in the function for individual umpires.

Update: Strike zones sharper outside than inside.