Nitpicking

I just happened to read a post on Fangraphs about the usefulness of the standard AVG/OBP/SLG "triple-slash" as a descriptive metric even in an age where there are all sorts of fancy offensive-evaluation metrics (the article mentions wOBA and wRC+ in particular, both Fangraphs creations which I'm not getting into here). In the course of doing so he mentions that, since AVG and SLG have the same denominator, you can subtract them and get something mathematically meaningful, in this case extra bases per at-bat (though he says extra bases per hit, which is wrong). This number is denoted ISO, short for "isolated power" and which I always pronounce as "iso-pop" in my head, for some obscure reason. Anyway, the point of this little blog post here is that ISO strikes me as a very strange way to go about measuring a player's pure power. Here's an example: suppose we have two players, one with a batting-average of .350 and a slugging percentage of .500, and another who's hitting just .220 but slugging .370. They both have an ISO of .150, but which one has more power? I'd say the guy with the abysmal average. Why? Because while the high-average guy is averaging 10 bases per 7 hits, or 1.43 bases per hit, the low-average guy is averaging 1.68 bases per hit. That's more raw power. ISO has the unfortunate quality that, while trying to isolate power, it is simultaneously including a bonus for the skill of not getting out, or at least of getting hits. You can subtract, but dividing makes more sense.