||Jaso's MLB Rank (out of 205)
min 400 PA
*Evidence suggests that K-BB is more meaningful for pitchers than K/BB. It's probably also true for hitters.
Let this soak in for a minute. Jaso was among the best in both BB% and K%, and led in both BB/K and BB-K (the top 5 in both included Albert Pujols and Joe Mauer). His plate discipline was obviously outstanding.
Given the information we have about sample sizes, it would appear as though Jaso's plate discipline is indeed his true talent level. Still, the sample sizes Pizza Cutter gave us are blanket sample sizes, and as those of you who are statistically inclined know, it takes more data to get safe p-values about data points that are further from the mean. Or, in normal terms, Jaso might still be a regression candidate despite the safe sample size because of how extraordinary his numbers are. We'll take a look at this after the jump.
First consider what history has to tell us. In an attempt to find similar hitters, I looked for other rookies from 1970 to the present day who put up BB%s above 14 and K%s below 15 over the course of at least 400 PA. B-Ref yielded just 3 results (which should drive home just how special Jaso's season was), who averaged BB%s of 14.7 and K%s of 12.2, nearly identical to Jaso's discipline numbers from last year. How did these hitters do the following year, after pitchers adjusted to them?
The first two hitters (Alvin Davis and Steve Ontiveros) continued their excellent plate discipline the following year, putting up very similar walk and strikeout numbers. The third, Gerald Perry, only saw 262 plate appearances the following year, presumably due to injury (I can't find any information on what happened). For his career, however, his BB% declined, but he maintained a very low K%.
While the past only provides us with a limited sample size, it certainly appears as though there's no reason to believe that there's historical evidence to suggest he can't maintain his plate discipline. This approach, however, is very impersonal, and although it's interesting, because of the limited sample size it is also of limited use. A more personal examination is possible, however, using Jaso's plate discipline statistics.
It's been generally observed that plate discipline statistics (swing/contact%s and the like) are a better predictor of future BB and K numbers than past BB and K numbers. Using the methodologies here and here, we would project Jaso's K% to be 11.4 and his BB% to be 13.5%. Assuming that his ability to hold off on pitches doesn't change and that pitchers don't pitch him too differently (not necessarily a safe assumption, but one that would be hard to account for), it looks like we can count on John Jaso to be an on base machine next year too.