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True Average (TAv) is a measure of total offensive value scaled to batting average. Adjustments are made for park and league quality, as such the league-average mark is constant at .260.
True Average incorporates aspects that other linear weights-based metrics ignore. Reaching base on an error and situational hitting are included; meanwhile, strikeouts and bunts are treated as slightly more and less damaging outs than normal. The baseline for an average player is not meant to portray what a typical player has done, but rather what a typical player would do if given similar opportunities. That means adjustments made for parks and league quality. True Average's adjustments go beyond applying a blanket modifier-players who play more home games than road games will see that reflected in their adjustments. Unlike its predecessor, Equivalent Average, True Average does not consider baserunning or basestealing.
Here is an example of the True Average spectrum based upon the 2009-2011 seasons:
Excellent - Miguel Cabrera .342
Great - Alex Rodriguez .300
Average - Austin Jackson .260
Poor - Ronny Cedeno .228
Horrendous - Brandon Wood .192
0.9 (from the article) is no longer a stationary number, but a scale based on current season runs. It's all the way up to almost 1.07 now, due to run scoring being so much lower than when Colin wrote this (from the link above):
From 1993 to 2009, you can figure TAv simply as:
0.260 + (RAA/PA)*.9
Now, we will be tuning those values slightly to match the batting average for that season, but other than
that, that’s the formula for TAv we will be using once the new stat reports are rolled out.
All that matters essentially is the computation of the initial R/PA values. When people ask about wOBA, most
of the time what they really care about is the values presented on Fangraphs, derived from this set of
linear weights developed by Tom Tango.
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