Calculating Baseball Stats - Power/Speed Number (PowSpd)

Power/Speed Number, a statistic developed by noted baseball author and analyst Bill James, combines a players Home Run and Stolen Base numbers into one number. James called Power/Speed Number a "freak show stat", as it has no real analytical value, for several reasons. Before we discuss these reasons, let's look at how the statistic is calculated. The formula is:

Power/Speed Number = 2 (HR x SB) / HR + SB

Power/Speed Number is displayed as a number with one digit after the decimal point.

Let's look at a real world example of how this statistic is calculated. In 2005, Alfonso Soriano of the Texas Rangers led the major leagues in Power/Speed Number. It was the 3rd time that Soriano had led the league in PowSpd. In 2005, he hit 36 Home Runs and stole 30 bases. To calculate Soriano's Power/Speed Number, the formula would be populated like this:

2 (36 x 30) / 36 + 30 = 2 (1080) / 66 = 2160 / 66 = 32.7 PowSpd

Bobby Abreu of the Philadelphia Phillies led the National League in PowSpd in 2005, racking up 24 Home Runs and 31 Stolen Bases for a Power/Speed Number of 27.1. 2005 was the second straight season that Abreu led the National League in PowSpd.

The highest single season Power/Speed Number was turned in 1998 by Alex Rodriquez, then of the Seattle Mariners. Rodriguez hit 42 Home Runs and stole 46 bases to record a PowSpd of 43.9.

The highest career Power/Speed Number belongs to Barry Bonds. Going into the 2006 season, Bonds had 708 career Home Runs and 506 career Stolen Bases for a career PowSpd of 590.19. Rickey Henderson is second on the career list at 490.4, followed by Willie Mays (447.1), Barry's father Bobby Bonds (386.0), and Joe Morgan (385.9).

As I mentioned above, PowSpd is not a particularly useful statistic from an analytical standpoint. There are several reasons for this. To have a good Power/Speed rating, a player must do both things well. A player with power but little speed or speed but little power will not do well on this metric. Also, a hitter's other power numbers, such as doubles and triples, are not counted in this statistic at all. The use of Stolen Bases without consideration towards Caught Stealing also gives no advantage to the players who steal bases at a high success rate when compared to those who steal high numbers of steals at a low rate. For example, in 2005 Soriano stole 30 bases and was only caught twice, a very impressive 93.7% success rate. If he'd been caught 15 times instead of 2 (a far less impressive 66.7% rate), his PowSpd Number would be no different.

As you can see, Power/Speed Number is an interesting statistic to consider, as it helps to highlight players who both hit Home Runs and steal bases, but it has rather severe limits when trying to draw any real conclusions about a player's value.