Basically, PC considers each pitch as a decision that the batter must make. When the batter makes a "correct" decision, he will swing and hit a pitch into play (the outcome is ignored; also, two-strike fouls are considered correct responses), or he will take a pitch that is a ball. But there are two ways a batter can make an incorrect decision. First, he can swing and miss (or foul, if less than two strikes) a ball that he thought he could hit (a false positive--note, this could still be a ball in the strike zone--PC can't discern that with his dataset). Or, he can take a strike that he thought would be a ball (a false negative).
Once he does this, PC reports two statistics. First, he reports "sensitivity," which is an indication of how often the batter makes the right decisions vs. the wrong decisions as defined above. The highest sensitivities top 1.00, while the lowest are around 0.2 or 0.3. Adam Dunn, in 2006, had a sensitivity of 0.48, which ranked him 404th out of 431 batters. This means that Dunn makes far more mistakes than correct choices in terms of how he responds to pitches.
The second statistic that PC reports is "response bias." This essentially tells you the direction in which a batter makes mistakes. High biases (over 1.00) indicate batters that tend to swing and miss a lot more than they take strikes. Low biases (below 1.00) indicate batters that tend to take a lot more strikes than they swing and miss. Adam Dunn's response bias was a fairly low 0.918. This indicates that he takes a lot more strikes than he swings and misses.
The overall view of Adam Dunn, therefore, is that of a hitter that makes a lot of mistakes with regards to when he should swing, usually because he's taking pitches that he "should be" swinging at. This is very consistent with most scouting reports on him, of course, but this is the first time that I've seen statistics that can really demonstrate this.
Whether you view Dunn as being very disciplined, or as being very reluctant to swing, is probably up to your definition of discipline. To me, it might indicate great patience (perhaps to a fault), but probably not good discipline.
Scott Hatteberg makes a very interesting contrast to Dunn. As you'll recall, Hatteberg's walk rate was second (at 14%) on the Reds last season to Dunn's (17%), yet his strikeout rate was the best on the team (just 8%). The net run value from Hatteberg's strike zone judgement (walks and strikeouts) was about four runs greater than Dunn's. So how does Hatteberg shake down in this new analysis?
According to PC's article, Hatteberg's response bias was the lowest in PC's study at 0.656. This indicates that Hatteberg was far more likely to take a strike than to swing and miss. But
his sensitivity was a remarkable 0.97, the 7th best in baseball. Therefore, Hatteberg made very few mistakes. When he swung at a pitch, he usually made contact and hit it fair, but when he took a pitch, it was more likely to be a ball than most other hitters in baseball.
I really like these new stats. They are a really interesting way of looking at how a hitter approaches his game. Hopefully someone can get them automated and we can see these data for other seasons, including the current one, at some point in the future. If nothing else, I'd love to see a spreadsheet reporting these values for all players in PC's dataset. :)
Update: Pizza Cutter has kindly posted his data in a google spreadsheet! Thanks! I'm looking forward to giving these data a look...once I get caught up on all the month-change events around here.
Photo by AP/Tony Tribble