Equivalent average
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Equivalent Average (EqA) is a baseball metric invented by Clay Davenport, and intended to express the production of hitters in a context independent of park and league effects. It represents a hitter's productivity using the same scale as batting average. Thus, a hitter with an EqA over .300 is a very good hitter, while a hitter with an EqA of .220 or below is poor. An EqA of .260 is considered league average.
EqA is one of several sabermetric approaches which validated the notion that minor league hitting statistics can be useful measurements of Major League ability. It does this by adjusting a player's raw statistics for park and league effects.
For instance, the Pacific Coast League is a minor league known to be a very friendly venue for hitters. Therefore, a hitter in the PCL may have notably depressed raw statistics (a lower batting average, fewer home runs, etc.) if he were hitting in another league at the same level. Additionally, in general the level of competition at the PCL is lower than that in the Majors, so a hitter in the PCL would likely have lesser raw statistics in the Majors. EqA is thus useful to strip certain illusions from the surface of players' raw statistics.
EqA is a derivative of REqA. REqA is (H + TB + 1.5*(BB + HBP) + SB + SH + SF) which is then divided by (AB + BB + HBP + SH + SF + CS + SB/3). REqA in turn is adjusted to account for league difficulty and scale to create EqA.
EqA is similar to Major League Equivalency (MLE), a metric developed by Bill James.
EqA has been used for several years by the authors of the Baseball Prospectus.