Where Pitches per Plate Appearance Matters Most

To finally alleviate my doubts about how important seeing many pitches per plate appearance is to a player's success, I decided to run some correlations between pitches per plate appearance and seven hitting statistics to see how closely linked everything is. The data I looked at is only for the 2006 season so should not be looked at as being indicative of every single baseball season, although I'm pretty sure the correlation coefficients follow the same pattern year in and year out.

For the three most accepted hitting statistics these days, batting average, on-base percentage, and slugging percentage, the lowest correlation to pitches per plate appearance belonged to batting average with a correlation coefficient of -0.109. This low number is in no way surprising because just as many hits come early in the count as later in the count so there is no disadvantage to free swingers there. Slugging percentage carried a correlation coefficient to pitches per plate apperance of .281, not particularly high showing the two variables are not that highly linked. As many might expect, of these three statistics, on-base percentage has the highest correlation coefficient, which is .525, showing those who see many pitches know not to swing at pitches out of the strike zone.

Even though the on-base percentage correlation coefficient established that pitches per plate appearance correlates well to it, I was still not satisfied so on a whim, I decided to subtract a player's batting average from his on-base percentage and see how well the difference was linked to pitches per plate appearance. The whim rewarded me with a correlation coefficient of .774, a pretty high number. So pitches per plate appearance may not provide a clue as to how high a player's batting average will be or even how high a player's on-base percentage will be, but you will be able to predict with some degree of confidence how high the difference between those two statistics will be compared to someone who doesn't see as many pitches per plate appearance. That knowledge will help teams obsessed with on-base percentage the most.

Correlation coefficients for the other hitting statistics I looked at are as follows: .434 (Gross Product Average), .441 (Weighted On-Base Average), and .347 (Isolated Power). Gross product average and weighted on-base average are both variations of OPS that attribute more weight to on-base percentage than slugging percentage, which explains why the correlation coefficients are lower than on-base percentage's but higher than slugging percentage's.