Wow. The obvious thing that jumps out here is how well pitchers do on close pitches in the ninth inning. Following up from my last article, I feel more confident suggesting that the quality of the pitcher plays a role in which way the calls go. Closers appear to get the benefit of the doubt, while the extras appear to be left to the back of the bullpen. I'd still like to think there's some sort of umpire fatigue that explains the extra innings too. It just seems too human an explanation to ignore.

I changed around the labels this time to try and make things more clear. It's now organized according to pitching team - so the positive number for the Home team is actually a positive benefit for the pitchers.

Beyond the change in labels, there's really no difference in looking at the edges versus all pitches - still a slight advantage to the home team.

The most surprising thing here is that the proportions for each age stayed pretty close from all called pitches to the pitches on the edge. I thought (and it was suggested by more than one person) that older pitchers would be be more likely to nibble and therefore we'd see a higher proportion of close pitches going to the elders. That's clearly not the case, as you can see even more clearly below. This means that the difference according to age is mostly composed of selection bias and umpires actually giving older pitchers the benefit of the doubt.

Looking at experience shows pretty much the same thing as age - which is what I'd expect since they're so closely correlated.

There's nothing too interesting in this comparison. Righties still have a slight advantage over lefties.

Again, nothing to see here. (I suppose I'm expected to say "Pass.")

There is a slight variation here in the percentage of total pitches for each category. Sure, .6% isn't very big, and could easily have no identifiable cause, but it does look like pitchers with good control have more called pitches near the edges. That's not very surprising of course, since they're likely going to have fewer called pitches well outside the strike zone (those are largely balls), which means more will be in or around the strike zone.

So even though the spread between best and worse is generally a lot bigger for the close pitches, the fact that they only happen about half as often drives the actual effect to be the same or less than for all called pitches. That's not to say that half the effect is from close called pitches and the other half from no-doubters. It looks like most of the mistakes, and most of the variation, occurs on close called pitches. However, there doesn't appear to be a whole lot of accuracy gained on the runs/game level by breaking out only the pitches on the edges.

That said, we did learn a few things. Surprisingly, there appears to be very little difference between age groups in the amount of called pitches that are near the edges. That seems to go against the conventional wisdom of older pitches starting to place their pitches more as they lose a little off their fastballs. I wonder how many pitchers really do make that transition successfully, and how many keep following the same strategy and either succeed (and not change) or fail (and retire). These numbers suggest not too many really do change their approach too much.

To wrap up, again I caution you against reading too much into these results. There's way too many unknowns and, even worse, known issues with the data and the criteria used to determine the splits to make them that useful. They can be used to start discussion and further research, but I definitely wouldn't try to work them into projections any time soon.