sabermetrics Sabermetrics (originally SABRmetrics) is the original or blanket term for sports analytics in the US, the empirical analysis of baseball, especially the development of advanced metrics based on baseball statistics that measure in-game activity ...

and basketball analytics, similarity scores are a method of comparing

baseball Baseball is a bat-and-ball games, bat-and-ball sport played between two team sport, teams of nine players each, taking turns batting (baseball), batting and Fielding (baseball), fielding. The game occurs over the course of several Pitch ...

and

basketball Basketball is a team sport in which two teams, most commonly of five players each, opposing one another on a rectangular Basketball court, court, compete with the primary objective of #Shooting, shooting a basketball (ball), basketball (appro ...

players (usually in

MLB Major League Baseball (MLB) is a professional baseball league composed of 30 teams, divided equally between the National League (baseball), National League (NL) and the American League (AL), with 29 in the United States and 1 in Canada. MLB i ...

or the

NBA The National Basketball Association (NBA) is a professional basketball league in North America composed of 30 teams (29 in the United States and 1 in Canada). The NBA is one of the major professional sports leagues in the United States and Ca ...

) to other players, with the intent of discovering who the most similar historical players are to a certain player. Similarity scores are among the many original sabermetric concepts first introduced by

Bill James George William James (born October 5, 1949) is an American baseball writer, historian, and statistician whose work has been widely influential. Since 1977, James has written more than two dozen books about baseball history and statistics. His a ...

. James initially created the concept as a way to effectively compare non-

Hall of Fame A hall, wall, or walk of fame is a list of individuals, achievements, or other entities, usually chosen by a group of electors, to mark their excellence or Wiktionary:fame, fame in their field. In some cases, these halls of fame consist of actu ...

players to players in the Hall, to see who was either on track to make the HOF, or to determine if any eligible players had been snubbed by the selection committee. For example, if the most similar players to a non-HOFer were all in the Hall of Fame, one could effectively argue that that player should be in the Hall. More recently, similarity scores have been used to determine career paths and projected statistics for players. The logic behind this line of thought is simple: players often follow similar career trajectories to their most similar players, so the historical similar players' performance in years after the active player's current age should be a good predictor of that active player's future production. An example of this would be the

Football Outsiders Football Outsiders (FO) was a website started in July 2003 which focused on advanced statistical analysis of the National Football League (NFL). The site was run by a staff of regular writers, who produced a series of weekly columns using both t ...

' discovery that all but the highest caliber of

wide receiver A wide receiver (WR), also referred to as a wideout, and historically known as a split end (SE) or flanker (FL), is an eligible receiver in gridiron football. A key skill position of the offense (American football), offense, WR gets its name ...

s suffer a marked decline after their seventh season in the NFL, a fact that bore out for the receivers selected in the

1996 NFL draft The 1996 NFL draft was the procedure by which National Football League teams selected amateur college football players. It is officially known as the NFL Annual Player Selection Meeting. The NFL draft, draft was held April 20–21, 1996 NFL seas ...

when their production collectively slipped. Aaron Schatz, "Hard Times for the Class of '96"
FootballOutsiders.com (July 8, 2004)
Many baseball analysts have augmented James' method over the years, or come up with their own system of measuring similarity. ''

Baseball Prospectus Baseball Prospectus (BP) is an organization that publishes a website, BaseballProspectus.com, devoted to the sabermetric analysis of baseball. BP has a staff of regular columnists and provides advanced statistics as well as player and team perf ...

'' employs a projection system developed by

Nate Silver Nathaniel Read Silver (born January 13, 1978) is an American statistician, political analyst, author, sports gambler, and poker player who Sabermetrics, analyzes baseball, basketball and Psephology, elections. He is the founder of ''FiveThirty ...

known as

PECOTA PECOTA, an acronym for ''Player Empirical Comparison and Optimization Test Algorithm'', is a sabermetric system for forecasting Major League Baseball player performance. The word is a backronym based on the name of journeyman major league player B ...

which applies nearest neighbor analysis to calculate similarities between players from different eras. ''Pro Football Prospectus'' (written by

) has their own system (dubbed "KUBIAK" after longtime Broncos backup

quarterback The quarterback (QB) is a position in gridiron football who are members of the offensive side of the ball and mostly line up directly behind the Lineman (football), offensive line. In modern American football, the quarterback is usually consider ...

Gary Kubiak) for projecting future performance. John Hollinger developed a similar system for basketball players in his ''Pro Basketball Forecast'' series of books, and several APBRmetricians have expanded on his methodology. Similarity scores are also used extensively in many statistical forecasting programs.

References

{{reflist

External links

Baseball Reference
which employs a similarity method much like James' original method
Basketball-Reference.com
which features a complex similarity-score system for NBA players
Football OutsidersBaseball Prospectus
which uses similarity scores in

that are calculated in a way that differs significantly from James' method.
Ken Pomeroy of Basketball Prospectus
who uses similarity scores for college basketball players. Baseball statistics Basketball statistics American football terminology Bill James