Who Are the Most Powerful Hitters in Baseball?

A few months ago, I reinvented an old novelty statistic called Power Factor that seemed to me to be a better way to measure raw power than the more popular Isolated Power. The formula is quite simple:

For reference, here's a quick percentile chart from last year:

via www.rantsports.com

In addition to its superior year-to-year consistency and predictive power of ISO (among batters with at least 400 PA's in both years, the correlation between 2009 PF and 2010 ISO was actually greater than that between 2009 and 2010 ISO), Power Factor removes the bias towards contact hitters and the heavy influence of BABIP swings that are inherent in ISO:

Let’s take the real-world example of 2010 teammates Carl Crawford and B.J. Upton. According to ISO, Crawford (.188) showed a little more power than Upton (.187). But did Crawford really outslug Upton, or was his extra-base edge simply a product of having more hits?

Of Upton’s 127 hits, 60 went for extra bases; Crawford managed 62 extra-base hits out of the 184 times reached he safely. Yes, Crawford had more extra-base hits, but a much higher proportion of Upton’s hits (47%) were doubles or better than Crawford’s (34%). An Upton hit was 50% more likely to go for extra bases than a Crawford base knocked, yet ISO said their power was virtually identical.

Given the choice between the two of them, player with a high ISO would generally be more useful than a player with a high PF—ISO makes more sense if you think of it as a measure of how well a hitter puts his slugging ability to use —but the latter would have more raw power.

So what do the 2011 Power Factor leaderboards look like? Here's the Top 25 list: (numbers as of Tuesday)

See anything surprising? Kelly Johnson and Mark Trumbo's names don't get thrown around much when talking about the most powerful hitters in the game. Prince Fielder is sandwiched between J.J. Hardy and Carlos Santana, with Danny Espinosa and Josh Willingham not too far behind. Adam Dunn still has terrific power. And perhaps most startlingly, Jose Bautista is not the most powerful player in baseball.

The bottom 10 should be a little less surprising:

Wondering who gets the biggest boosts from using ISO or PF? Here are the players who ISO overrates most, as determined by the difference between their ranks on the ISO leaderboards and their positions on the PF charts:

And the players ISO most underrates:

You'll notice that each list has its own distinct type of player: the overrated list is populated with sluggers who also happen to be very good pure hitters, while the underrated list includes several players who many would consider to be generally pretty bad, at least this year—which is exactly what we'd expect given the differences between the two formulas. Essentially what this means is that some portions of what we think of as Joey Votto and Miguel Cabrera's power are actually just their good contact skills and plate discipline. Similarly, when we look at declining guys like Dunn and Lyle Overbay, their diminished slugging abilities are caused more by their inabilities to put the bat on the ball than declines in their raw power.

Again, it's important to note that possessing power (i.e., having a high Power Factor) isn't nearly as important as being able to harness it (i.e., having a high ISO). Even if their raw power is overrated, high-ISO guys are generally much better than high-PF players—if they were hitting off a tee perhaps Vernon Wells and Justin Smoak would be All-Stars, but as it stands no one in their right mind would choose them over Jacoby Ellsbury and Jose Reyes.

So the next time someone tells you that Adrian Gonzalez should be the AL MVP, remember that—according to these numbers, at least—he has less raw power than Miguel Olivo.