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Monday, May 09, 2011
Reader Mail of the minute: apparent vagaries in wOBA
1. IBB, NIBB, HBP: why the different coefficient values for each?
Hit batters occur more randomly than NIBB. IBB occur in a very non-random fashion. So, because a hit batter occurs more often when it can actually move a runner from 1B to 2B, it gets a slightly higher weight.
The implicit coefficient value of the IBB is around 0.33. (It’s actually dynamic, according to the performance of the player, and a player with a .400 wOBA overall has an implicit coefficient of .40 for the IBB.) If you ignore the IBB in both the numerator and denominator, you’d get the implicit coefficient for the IBB: it’s the batter’s wOBA.
2. Why errors for batters?
When hitters reach base on error, they actually reached base safely. This is a good thing. In terms of IMPACT, reaching base on error is a bit more valuable than reaching base on a single (because of multi-base errors). As for the “cause” of the error: yes, the batter’s identity is more reflective of the single than of reaching on error. But, we don’t care about that. We only care about the results of events, not the reason for the events. If we cared for the reasons, we’d overweight the HR and BB and underweight the single and double (because the identity of the player is more important for HR and BB, and SO).
3. What about steals?
If you need it, give SB a .25 and CS a -.50, in the numerator. Don’t touch the denominator. If you don’t need it, don’t put it in.
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Related thread:
http://www.insidethebook.com/ee/index.php/site/comments/the_history_of_the_woba_part_1/
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