K/9 or K%?

Yesterday, Chris Constancio, over at FirstInning, posted an interesting argument against K/9 and BB/9, statistics that I've been using quite often on this blog.  K/9 is strikeouts per 9 innings, while BB/9 is walks per 9 innings.

Constancio writes that K% and BB% (percentage of strikeouts and walks per batter faced) "are better descriptors of pitchers' skill in striking out batters and avoiding walks."  He's right, of course. He explains further: "Pitchers who do surrender many hits or walk a lot of batters have inflated K/9 rates because they face more batters per inning and therefore have more opportunities to record strikeouts...K% and BB% do a better job of isolating the skills they measure, so it should come as no surprise that K% and BB% are more strongly correlated from season-to-season than K/9 and BB/9."

The problem with using K% and BB% is the statistic "total batters faced" (needed to compute K% and BB%). While firstinning.com carries the stat for minor league players, most college team statistics pages do not list TBF, adding several more computations than a standard K or BB/9.   

Therefore, faithful readers, I'll need to continue to use K/9 and BB/9.... for college players, anyway.

Comments

[Chris C.]

A good decision.

Like I write, the difference between K/9 and K% is minor in most cases. If you have total batters faced, there is no reason not to use K% and BB%. If not, it's good enough to use K/9 and BB/9 while mentioning cases when the numbers might be inflated/deflated due to extreme pitchers.

[JohnLL]

Thanks, Chris. I'm not a statistician, so I'm feeling my way through stat issues on this blog, but your explanation made immediate sense. (Sometimes the explanations on Baseballprospectus make my head swim...)
Onward ho...