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baseball prospectus glossary wrote:Comparable Players are the backbone of a player's PECOTA. Only the twenty best comparables are listed here, but as many as 100 players may be used in the generation of his forecast if they are sufficiently comparable.
PECOTA compares each hitter against a database of roughly 20,000 major league batter seasons since World War II. In addition, it also draws upon a database of roughly 10,000 translated minor league seasons (1998-2005) for hitters who spent most of their previous season in the minor leagues. (When minor league comparables are used, they appear in ALL CAPS). PECOTA considers four broad categories of attributes in determining a hitter's comparability:
1. Production metrics--in particular, batting average, isolated power, unintentional walk rate, strikeout rate, groundball:flyball ratio and a modified version of the Bill James speed score.
2. Usage metrics, including career length and plate appearances.
3. Phenotypic attributes, including handedness, height and weight.
4. Fielding Position. PECOTA doesn't require that a comparable hitter play the same defensive position; it is a factor that is evaluated along with many others, and assigned a relatively substantial weight. Consideration is also given to the 'similarity' between two positions; for example, a shortstop will be compared to a second baseman before he is compared to a left fielder. (See additional discussion).
PECOTA compares each pitcher against a database of roughly 15,000 major league pitcher seasons since World War II, and 10,000 minor league pitcher seasons from 1998-2005. Pitchers are compared only against others of the same age. PECOTA considers three broad categories of attributes in determining comparability:
1. Production metrics such as strikeout rates, walk rates, isolated power and batting average against, and groundball:flyball ratio.
2. Usage metrics such as career length, total batters faced, and percentage of innings pitched in starting/relief.
3. Phenotypic attributes, including handedness, height, and weight.
In most cases, the database is large enough to provide a meaningfully large set of appropriate comparables. When it isn't, the program is designed to 'cheat' by expanding its tolerance for dissimilar players until a reasonable sample size is reached. In the case of very old or very young players, there may not be a significant number of pitchers who appeared in the major leagues at all at that age, and so the results of their forecast may be unreliable.
WittyC wrote:I have two questions...
1) Do the books provide any different info than the website, or is it just a matter of convenience?
2) Do subscribers actually have access to the formula they use, or is it a big family secret like the KFC recipe?
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