Isolated power

Isolated Power is a sabermetric statistic that attempts to describe a hitter's overall effectiveness by measuring his ability to generate extra base hits. ISO was apparently created by baseball great Branch Rickey in the 1950’s (along with Allan Roth, they apparently created the idea, though they termed it “Power Average”). ISO is figured by the simple equation:

ISO = Slugging % - Batting Average

EXAMPLE

Why ISO? Let’s take a look at the following hypothetical player. PLAYER A: .300 AVG., .400 OBP (On Base Percentage), .500 SLG

AVG tells you that in this case player “A” generates a hit 3 out of 10 times he records an at bat. (H / AB)

OBP tells you that that “A” reaches base 4 out of 10 times he records a plate appearance. (H + BB + HBP) / (AB + BB + HBP + SF)

SLG tells you that “A” generates 5 bases, on hits, per 10 times at bat. (TB / AB).

ISO tells you that “A” generates 2 extra bases per 10 times at bat. (SLG% - AVG)

AVG measures all hits without any attention being paid to what type they are. SLG% measures all bases earned including singles. Only ISO measures only extra base hits while excluding the other hits. Therefore, ISO is a good tool to measure the extra base potential, and thereby the run damage, that a hitter can produce for his team. ISO is also useful because it measures extra base hit totals without being totally dependent on the HR category.

One last note: the historical average for ISO is around .120, with .080 being roughly equivalent to a singles hitter, and anyone over .200 being considered a power hitter.