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Saturday, November 23, 2002

Nice Move, DIPShit

I went back to playing around with the pitching spreadsheet I used to calculate my DIPS numbers referred to in the article below, and discovered that I made an error in calculating the Yankee park factor. Basically, I transposed two digits for the Yankee home at-bat total, which should have been 2907 instead of 2097. Needless to say, those missing 810 ABs change things a bit. In this case they take the Yankee Stadium Park HR Factor from 1.054 to 0.968, and slightly lower the Yankee starters' DIPS ERAs by a few points. So I'll rerun that last chart:
             ERA   dERA   BABIP

Pettitte   3.27   3.28   .317

Clemens    4.35   3.34   .316

Mussina    4.05   3.73   .290

Hitchcock  5.49   3.81   .373 

Wells      3.75   3.87   .284

Hernandez  3.64   3.91   .264 

Weaver     4.04   4.11   .283 (NY only)

Weaver     3.52   3.81   .280 (TOT)

Yankees    3.87   3.71   .293

League     4.46   4.46   .290
The change is most apparent in the more homer-prone Yankee pitchers; Mussina, Weaver, and Hernandez all lower their dERA by more than a tenth of a run. And the team's dERA goes down to 3.71, compared to their 3.87 ERA, showing a bit more clearly how the below-average Yankee defense against balls in play cost the team a few runs here and there. Also note that I calculated full-season dERA for Weaver because I finally got around to calculating the Comerica Park HR Factor.

These new figures don't alter any of the other observations I made, but I might as well add a few other notes about the process, while I'm revisiting the calculations:

1. Team stats for the Yanks were taken from ESPN.com. League stats were taken from ESPN.com and MLB.com, with the latter figures used in case of any discrepancy.

2. I used actual Batters Faced Pitching numbers from those sources, rather than estimating as Voros McCracken does in his step-by-step instructions.

3. When I calculated the Yankee team DIPS, I adjusted for lefties by multiplying the LH correction factor by the percentage of innings pitched by Yank southpaws. This wasn't explicit in Voros' instructions, but it seems like the correct approach.

4. When I calculated the "League" DIPS for that chart, I DID NOT make any adjustment for lefthanded pitchers or knuckleballers, or for park factors (which would probably end up being close to 1, but not exactly so, depending upon the AL/NL balance of homers in interleague games) Thus, that number is probably off by a few points.

5. Voros' method for computing the Park Factor, which he graciously walked me through via email and has given me permission to pass along:
Here's a simple method using Home Runs per AB-SO:

HAB = Home at bats
RAB = Road at bats
HSO = Home Strikeouts
RSO = Road Strikeouts
HHR = Home Home Runs
RHR = Road Home Runs
AB = Total At Bats
SO = Total Strike Outs
HR = Total Home Runs.

The first thing you do is calculate the "actual" rate of

Actual Rate = HR/(AB-SO).

This is the rate to compare to, and how you'll get the factor. After you get that, and let's say it is .041, you now make the more complicated calculation:

Note: For NL and AL teams there is a difference. The below will be for AL teams. For NL teams change the "7"s to "8"s and the "13"s to "15"s. The reason is that what you're doing is estimating what the stats would be if the Yankees played 1/14 th of their games in Yankee Stadium instead of 1/2 (or 1/14 divided by 1/2 equals 1/7):

Adjusted Rate = ((HHR*(1/7))+(RHR*(13/7)))/(((HAB-HSO)*(1/7))+((RAB-RSO)*(13/7)))

Now you'll get a number like the simple calculation above but different. Let's say it is .043

The rest is easy. If you want to adjust numbers from Yankee Stadium to a neutral park then:

Park Factor = Adjusted Rate/Actual Rate

In this case it would be .043/.041 = 1.0488.

So if you have a pitcher whose rate of HR/(BFP-HP-BB-SO) is .025 you multiply .025 by 1.0488 for his Park Neutral rate or:

1.0488 * .025 = .0262
I'm working on calculating DIPS numbers for some of the select free-agent starters as well as other names that have popped up in Yankee trade talks. Anybody with a line on an easy way to gather home and road splits for AB, HR, and SO (all needed to calculate Park Factors) or the willingness to do so themselves, drop me a line.
--posted by Jay at 5:02 PM LINK

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