Isolated Power is a very rarely used Baseball statistic. Unlike most very rarely used Baseball statistics, it was not created by Bill James; rather, it was invented by the creator of On-Base Percentage, a more often used statistic, Branch Rickey.
Isolated Power measures a hitters ability to get extra bases on a hit. It can be measured by subtracting a player's batting average from his slugging percentage. The all-time leader is Babe Ruth, with .348, extremely high considering his career batting average was a good deal higher than your average power hitter of today.
All time IP leaders
* - active
- Babe Ruth, .348
- Mark McGwire, .325
- Barry Bonds*, .300
- Lou Gehrig, .292
- Hank Greenberg, .292
- Ted Williams, .289
- Jimmie Foxx, .284
- Manny Ramirez*, .283
- Jim Thome*, .280
- Ralph Kiner, .269
Single Season IP
* - active
- Barry Bonds*--2001--.536
- Babe Ruth--1920--.472
- Babe Ruth--1921--.469
- Mark McGwire--1998--.454
- Barry Bonds*--2002--.429
- Mark McGwire--1996--.418
- Mark McGwire--1999--.418
- Babe Ruth--1927--.417
- Sammy Sosa*--2001--.409
- Lou Gehrig--1927--.392
sources: http://www.baseballimmortals.net/ , http://www.baseball-almanac.com