Tuesday, November 04, 2008
Reconciling Linear Weights and Runs Created
Pure math post, but no mathematical gymnastics:
I took a standard hitting line and I call that my BASE hitting line. By definition, the Linear Weights is zero.
I create 2 individual profiles of players:
- RICE (which is the same as BASE, but the walks are set to 0, and the HR is set higher, to force the Linear Weights to zero); the slash line is: 0.269 0.273 0.519
- PIERRE (which is the same as BASE, but the HR are set to 0, and the walk is set higher, to force the Linear Weights to zero); the slash line is: 0.269 0.382 0.335
As you can see the RICE player gets tons more outs per PA than the PIERRE player.
According to Linear Weights, they are both identical.
Anyway, I added RICE to 8*BASE and ensured:
1. RICE’s PA was one-ninth the total
2. RICE + 8*BASE totalled 27 outs
I did the same for PIERRE.
I ran both teams through BaseRuns. I get the following:
RICE’s team: 4.946 runs per 27 outs
PIERRE’s team: 4.957 runs per 27 outs
The BASE team: 4.953 runs per 27 outs
We see therefore that, if BaseRuns is to be believed, that means Linear Weights overcredited RICE’s team by .007 runs per 27 team outs. If we give him 150 games, that means 1 run.
Similarly, if BaseRuns is to be believed, then LWTS undercredited PIERRE’s team by .004 runs per 27 team outs, or 0.6 runs per 150 games.
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Now, let’s try it by adding in a great hitter (I’ll call these guys RICE+ and PIERRE+). These are the two slash lines that give me the same Linear Weighs per PA:
0.269 0.273 0.714
0.269 0.498 0.335
If I add each of these guys to the BASE team, I get these runs per game:
5.20 RICE+
5.24 PIERRE+
This difference is .038 runs per 27 team outs. The true gap should be 5.7 runs per 150 team games, according to BaseRuns, but Linear Weights per PA says 0.
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Now, instead of the same Linear Weights per PA, let’s force it as the same Linear Weights per Out. Here are the slash lines:
0.269 0.273 0.714
0.269 0.450 0.335
I’ll call these guys RICE- and PIERRE-. In this case, Linear Weights per PA says that RICE- is much better, to the tune of 15 runs per 150 team games. Linear Weights per out says that they are equals. What does BaseRuns say?
5.20 RICE-
5.12 PIERRE-
In this case, you get .08 runs per game difference, or 12 runs per 150 team games.
I’ve got my spreadsheet up. Tell me what you’d like me to run…
Now, let me try it by forcing the same 5.20 runs per game.
Our two hitters have an EQUAL impact to team runs per 27 outs, with the following:
Linear Weights per out:
.082 RICE
.100 PIERRE
And Linear Weights per PA:
.060 RICE
.052 PIERRE
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Also note that the PIERRE team gets 1.44 more PA per 27 team outs (and 0.16 more PA for himself).
If we take .052 times .16 we get… .008. That’s the difference to make up between him and RICE.
So, the reconciliation starts with Linear Weights per PA, and then you have a further adjustment for the extra PA that he gets over RICE.
And that should conclude that!
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I’ll give you the short-hand formula as soon as I can…