FantasyPros has put together a glossary of sabermetrics statistics for readers to reference. Deeper statistical analysis is being used by fantasy players more and more in daily and season-long leagues. We’re providing the glossary so that you can easily reference what the stats we use in our articles refer to and how they should be used for fantasy baseball purposes. Below we’ll take a look at ISO.
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The purpose of the sabermetric stat Isolated Power (ISO) is to represent the raw power of a hitter. The formula the stat uses is slugging percentage minus batting average. Slugging percentage is total bases divided by at-bats, while batting average is hits divided by at-bats. It measures how many extra bases a player achieves per at-bat. A player who hits all singles would register a .000 in ISO, but a player who homers every at-bat would earn the maximum of 3.000.
ISO tells you the average number of extra bases a player earns per at bat. This is information you want to know in fantasy. You want to know how many of a player’s hits are singles and how many are extra-base hits. The more extra-base hits, the more likely a player will accumulate RBI and runs. ISO doesn’t tell you anything you can’t learn from batting average and slugging percentage together, but it saves you the extra step.
In fantasy leagues, home runs are one of the categories that players need. ISO can be used to help isolate which hitters are power hitters, therefore, more likely to provide home runs for your fantasy team. The higher an ISO rating, the more extra bases a batter achieves per hit. An elite power hitter would carry a .200-plus ISO while even a high-average singles hitter could carry a sub-.100 average. An average hitter maintains a .150 ISO average.
To draw any conclusions about the future power ability of a hitter using ISO, a large sample size of at-bats is needed. It is recommended to look at ISO only in conjunction with a sample size of over 500 at-bats. A player early on in the season can carry an ISO of .400, but that is not indicative of their power ability or future ISO rating.
Also, ISO should be used in conjunction with a batting average to be used effectively. If Player A hits .300 with a .500 slugging percentage, he will register the same ISO factor as Player B hitting .200 with a .400 slugging percentage even though they are obviously not equal.
Dale Redman is a correspondent at FantasyPros. To read more from Dale, check out his archive and follow him @fantasytool.
