from Amazon
Wednesday, April 23, 2008
What in the world is OBP minus BA?
Patriot tells us:
Walks/PA is what you are after…the player’s walk rate. But OBA-BA multiplies walk rate by one minus BA. So if you have two guys who each draw 50 walks in 550 PA, but one gets 150 hits (.340) and one gets 135 hits (.270), the one with the lower BA has a higher OBA-BA, .066 to .060.
It is remarkably lazy to leave it in the form OBA-BA. You can very easily get walk rate from (OBA - BA)/(1 - BA).
Here’s more to back up Patriot:
AB H BB BA OBP OBP-BA Patriot Tango
450 100 50 0.222 0.300 0.078 0.100 0.092
450 125 50 0.278 0.350 0.072 0.100 0.079
450 150 50 0.333 0.400 0.067 0.100 0.069
450 175 50 0.389 0.450 0.061 0.100 0.061
450 200 50 0.444 0.500 0.056 0.100 0.055
450 225 50 0.500 0.550 0.050 0.100 0.050
“Patriot” is (OBP-BA)/(1-BA). As you can see, exactly .100 in all cases. That’s the same thing as doing BB/PA.
“Tango” is BB/(H+BB)*.275. As you can see, a fairly strong match to OBP-BA.
So, Patriot it right. If you are trying to infer the walk rate, take your OBP-BA and then divided by 1-BA.
But, if you have some ulterior motive behind using OBP-BA, it is really alot more aligned in terms of your “profile” or ratio of walks to hits. So, it is not your “walk” rate, but your walk rate relative to your hits. Or something.
I am guilty of doing this, and it was out of sheer laziness. Shame on me, and thanks Patriot.