Thursday, February 14, 2008

Quantifying consistency

You often hear fans, announcers, players and others talking about the consistency of various hitters. Some hitters are said to stay steady from the beginning of the season to the end. Others are known as streak hitters who go hot and cold throughout the year. Some think that consistent hitters are more productive than streak hitters and that they are more likely to continue hitting in the future. It also believed by some that consistency is a skill that repeats itself from year to year rather than just a random thing. Before we can explore these and other issues, it is necessary to quantify consistency and that is what this post is about.

Using the retrosheet play by play databases, I divided the typical 180 day season (including days off) into roughly 18 nine day intervals. For each batter I calculated the Gross Production Average (GPA) in each interval. GPA is similar to OPS except that it weights the on base percentage (OBP) and slugging (SLG) more appropriately (OPS puts too much weight on slugging). It is calculated as follows:

GPA = (1.8*OBP + SLG)/4.

Besides weighting things more correctly, GPA is appealing because it is scaled similarly to batting average. If a GPA looks like it would be a good batting average (e.g. .315), then it's a good GPA.

Placido Polanco's GPA is tracked by interval in the chart below. You can see that his GPA rarely strayed too far from his season average. In contrast, the chart for Pudge Rodriguez shows that his GPA by interval was much more variable. To quantify this variability, I used something called the coefficient of variation (CV). For the statistically inclined, the CV is the standard deviation of the 18 data points divided by the average of the 18 data points times 100.

More simply, players with low CVs are more consistent than players with high CVs. Polanco had a CV of 16.9 and Rodriguez was at 37.5 in 2007. .I calculated the CV for every player with at least 14 intervals where he had at least 20 plate appearances. There were 194 major league qualifiers in 2007 and their CVs ranged from 13.9 to 48.9.


Table 1 below lists the Tigers in order from least consistent to most consistent. The most consistent Tigers in 2007 were newly acquired Edgar Renteria, Placido Polanco and Carlos Guillen. The streakiest Tigers were Pudge Rodriguez, Brandon Inge and Gary Sheffield.

Table 2 includes the most consistent hitters in the major leagues in 2007. Renteria also tops that list followed by Chipper Jones and Chase Utley. Table 3 includes the streakiest hitters. Leading that group are Dioner Navarro, John Buck and Andrew Jones.

In a future post (more than one if it gets interesting), I'll compare the characteristics of consistent hitters and streak hitters, examine the repeatability of the the GPA CV stat and look to see if it is predictive of future production in any way.
The information used here was obtained free of charge from and is copyrighted by
Retrosheet. Interested parties may contact Retrosheet at "www.retrosheet.org".



Table 1: Consistency of Tiger batters in 2007

first name

last name

PA

GPA

CV

Edgar

Renteria

543

.292

13.9

Placido

Polanco

641

.289

16.9

Carlos

Guillen

630

.286

22.8

Curtis

Granderson

676

.299

24.7

Jacque

Jones

495

.250

27.2

Magglio

Ordonez

679

.344

27.5

Miguel

Cabrera

680

.321

29.1

Sean

Casey

496

.257

30.3

Gary

Sheffield

593

.285

36.8

Brandon

Inge

577

.233

37.3

Ivan

Rodriguez

515

.237

37.5



Table 2: Top ten most consistent hitters in majors in 2007

first name

last name

PA

GPA

CV

Edgar

Renteria

543

.292

13.9

Chipper

Jones

600

.342

13.9

Chase

Utley

613

.326

14.5

Carlos

Ruiz

429

.250

16.4

Aramis

Ramirez

558

.302

16.6

Placido

Polanco

641

.289

16.9

Victor

Martinez

644

.298

17.3

Prince

Fielder

681

.332

17.4

Ichiro

Suzuki

737

.288

17.9

Aaron

Rowand

684

.296

18.0


Table 3: Least consistent hitters in majors in 2007

first name

last name

PA

GPA

CV

Dioner

Navarro

434

.215

48.9

John

Buck

399

.246

46.5

Andruw

Jones

659

.243

40.1

Mike

Jacobs

460

.257

40.1

Jack

Wilson

535

.266

39.9

Casey

Kotchman

508

.283

37.5

Ivan

Rodriguez

515

.237

37.5

Carlos

Pena

612

.341

37.5

Brandon

Inge

577

.233

37.3

Chris

Duncan

432

.279

36.9


The information used here was obtained free of charge from and is copyrighted by
Retrosheet. Interested parties may contact Retrosheet at "www.retrosheet.org".

2 comments:

  1. Nice work. I really like the whole concept behind this. You should consider taking your best sabermetric posts and throwing them into an ebook.

    While I'm not usually the biggest fan of the GPA (I think it gives too much credit to weaker hitting, obp players: ie, Brian Giles .289, Polanco .295) this is a great little study. I was surprised to see Carlos Pena in the 10 least consistent category after his huge 2007. I'm sure the fantasy guys would be all over info like that.

    ReplyDelete
  2. Thanks for reading my blog. I'm still not sure what's going to come out of this particular study. It looks like consistent hitters have better overall production on average. I'm not sue how predictive it is yet. I need to do some more analyses.

    I'm not wedded to GPA. It does work better than OPS at the team level but it's not something I've used that often. I typically use RC but I wanted to try something different.

    ReplyDelete

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