Saber-Friendly Tip #2: Talkin’ About Power
by Steve Slowinski - May 23, 2011
In case you missed the first article in this series — in which I talk about another way to look at BABIP — I’m trying to take a look at alternative ways to present sabermetric stats, in order to best represent them to an audience.
When you stop and think about it, despite the numerous baseball statistics out there, there are only a few limited ways of talking about a batter’s power. While there are a multitude of options when talking about plate discipline — On-Base Percentage, walk rate, outside swing rate, etc. — there are only a handful of widely available stats to use for power: the old standby, Slugging Percentage; a player’s raw total of homeruns or extra base hits; or the sabermetric alternative, Isolated Power.
So when you want to talk strictly about how powerful a player has been, which stat do you use? There are pluses and minuses to each of these stats, but do any of them necessarily stand out from the others? I’d argue no.
Slugging Percentage
The Good: Everyone knows it. It’s simple, easy to understand, and we all grew up using it.
The Bad: Like mentioned above, the formula of Slugging Percentage is very simplistic; it’s a player’s total bases divided by at bats. But if we’re talking about power, why are we including singles in the calculation? And if we’re putting value onto extra base hits, is a homerun worth twice what a double is worth?
Raw Homerun or Extra Base Hit Totals
The Good: Using the raw totals don’t attempt to place any value on each of the different hits, like Slugging Percentage does. Also, baseball fans don’t need to be told that 30+ homeruns is very good.
The Bad: Homeruns is just one part of the picture; doubles and triples are also very important. And if you list a player’s total extra base hits, you then run into the problem that you’re considering doubles as important as homeruns. Who’s the more powerful batter: someone who hits 30 doubles and 0 homeruns, or someone that hits 25 homeruns and 5 doubles?
Isolated Power (ISO)
The Good: It’s also a very simple statistic: Slugging Percentage minus Batting Average. This corrects for one of the flaws of Slugging Percentage, since this subtraction removes singles from the equation and leaves just the extra bases. As a result, Isolated Power gives more value to hitters that accumulate lots of extra bases but don’t hit for a high batting average.
The Bad: It’s on a funky scale. It’s a three-decimal stat, so I expect it to be on the same sort of scale as OBP or AVG, but it’s not. Instead, an average ISO score is around .145 and power hitters normally crack .200. It took me a long time to feel comfortable enough with the scale to begin using it in my writing, and new readers could have a problem with it.
***
I’ve gone back and forth on this question. Do I use a familiar stat, like Slugging Percentage, or do I go with Isolate Power — a stat that’s slightly more rigorous, yet is on a confusing scale for new readers? Believe it or not, the two stats correlate at a very high rate (.90 so far this season), so in general, you’re not losing much in terms of accuracy if you choose to use Slugging Percentage instead of Isolated Power. ISO is still an important statistic to use, since it can show you if a player might be over- or under-rated due to Slugging Percentage, but in the majority of cases the difference between the two stats isn’t as large as you may think. Power isn’t a very subtle skill; it tends to shine through no matter what lens you look at it through.
If you’re looking for a more rigorous alternative to Slugging Percentage, though, I’ve recently started looking at a player’s percentage of extra base hits. Consider:
Both these percentages tell you slightly different things — one tells you how often a player gets an extra base hit when they step to the plate, while the other tells you how often a player rips the ball deep when they get a hit — but they can both be useful when trying to get a full picture of a player’s power. Instead of limiting ourselves to just the handful of stats out there right now, why shouldn’t we use percentages like this, much like we’d use walk rate as an alternative to OBP? Both these stats correlate a high amount with Isolated Power (.91 for XBH/AB and .83 for XBH/H), so you know that they’re telling you similar information, but just in a different form.
I probably sound like a broken record, considering I finished the BABIP article on a similar note, but which stat you use depends on your audience and what questions you want to address. So don’t limit yourself to only Isolated Power; Slugging Percentage shouldn’t be throw out in the wash, as it has its many positives going for it as well. And don’t be afraid to branch out into some of the different percentage stats; they take but the work of a minutes to calculate, they are easy for new readers to understand, and they add nuance to your analysis.
