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".