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posté par Anonyme : | Anonyme a dit : C'est quoi le Win Shares ?
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Martin
Win Shares is a book (ISBN 1-931584-03-6) about baseball written by Bill James and Jim Henzler, published by STATS, Inc. in 2002.
As ESPN's Jim Baker put it, "we've been talking about Win shares, the baseball metric Bill James introduced in .... a book titled, oddly enough, Win Shares.[1] It explains the concepts of win shares, a baseball statistic. It takes a sabermetric approach to evaluating the contribution of individual players to their teams' overall performance, and focuses primarily on the many formulae involved in computing the final number of win shares accumulated, as well as presenting many lists of players ranked in various ways using the rating.
Baseball author and columnist Rob Neyer, writing for ESPN, called the book "groundbreaking".[2] Glenn Guzzo echoed him in The New Ballgame: Baseball Statistics for the Casual Fan, calling it a "groundbreaking volume".[3] In A Mathematician at the Ballpark: Odds and Probabilities for Baseball Fans, Professor Ken Ross describes the book as "erudite and interesting".[4] John Erardi of The Cincinnati Enquirer referred to it, while discussing some of its, conclusions as James' "acclaimed book".[5]
Leigh Grossman, in The Red Sox Fan Handbook: Everything You Need to Know to Be a Red Sox Fan Or to Marry One, called it "a book that statheads had been anticipating for years."[6] In the Seattle Post-Intelligencer, David Andriesen wrote of the book:
James, our foremost sabermetrician (a made-up word that means "guy who uses mathematics to study baseball"), has spent years developing a system called "win shares" a number that at its most basic level represents how many victories a player created for his team. His book on the system, titled "Win Shares," was recently published ... The result is a simple number. The method used to arrive at the number is enough to make John Forbes Nash pound his head against a brick wall.[7]
The Oakland Tribune pointed out, however, that it took James more than 100 pages in the book to explain his formula.[8] Bill Felber, in The Book on the Book: An Inquiry Into Which Strategies in the Modern Game Actually Work, compared James' philosophy as to use of relievers in the book, with those he endorsed as a Boston Red Sox executive.[9]
Hardball Times noted that based on reader responses, it appeared that the book was well received, and detailed what it liked and disliked about it,[10] and Dave Studeman wrote for it:
When Bill James rolled out his Win Shares opus, he included a chapter called "Win Shares and Replacement Level (Or...Pandora, shut your trap)." In that chapter, he conceded that the Win Shares work wasn't quite done, that Replacement-level Win Shares were a logical next step. But the extra work would be complex, and James wasn't quite ready to tackle it at the time. So this past winter, I gave it a shot.... I didn't address all the issues that Bill James raised in his book, but I think I came up with a decent approach.[11]
Keith Scherer of ESPN measured the Chicago White Sox defense by it, writing: "Jorge Orta is the only second baseman in history to get an F for his defense in Bill James' book, Win Shares."[12] In a later article for ESPN Scherer pointed out that "when Bill James published his book about Win Shares, he contemplated using the method to study the draft."[13] The Concord Monitor noted that at a game "A few ultradedicated fans even sit in the back row with their Bill James books and calculators tabulating Mainers win shares".[14]
In Practicing Sabermetrics: Putting the Science of Baseball Statistics to Work, by Gabriel B. Costa, Michael R. Huber, and John T. Saccoman, the authors discuss how James provides both a short form method and a long form method for calculation in his book, and that the easier short form method appears to work well for years after 1920.[15]
Dayn Perry notes in Winners: how good baseball teams become great ones (and it's not the way you think) how James points out correctly in the book that when a first baseman gets an assist for throwing to a player other than the pitcher, it is almost always a vital play.[16]
The Bill James Historical Baseball Abstract, 2001 edition, also written by James, uses win shares to evaluate the careers of many players, and to place them in contexts where they can be compared. The two books are effectively companions to one another.
Contents
1 Concept
1.1 Criticism of win shares
1.2 Basketball
2 References
Concept
Win shares is the name of the metric developed by James in his book. It considers statistics for baseball and basketball players, in the context of their team and in a sabermetric way, and assigns a single number to each player for his contributions for the year. A win share represents one-third of a team win, by definition.[17] If a team wins 80 games in a season, then its players will share 240 win shares. The formula for calculating win shares is complicated; it takes up pages 16–100 in the book. The general approach is to take the team's win shares (i.e., 3 times its number of wins), then divide them between offense and defense.
In baseball, all pitching, hitting and defensive contributions by the player are taken into account. Statistics are adjusted for park, league and era. On a team with equal offensive and defensive prowess, hitters receive 48% of the win shares and those win shares are allocated among the hitters based on runs created. An estimation is then made to decide what amount of the defensive credit goes to pitchers and what amount goes to fielders. Pitching contributions typically receive 35% (or 36%) of the win shares, defensive contributions receive 17% (or 16%) of the win shares. The pitching contributions are allocated among the pitchers based on runs prevented, the pitchers' analogue to runs created. Fielding contributions are allocated among the fielders based on a number of assumptions and a selection of traditional defensive statistics.[18]
In Major League Baseball, based on a 162-game schedule, a typical All-Star might amass 20 win shares in a season. More than 30 win shares (i.e. the player is directly responsible for 10 wins by his team) is indicative of MVP-level performance, and 40+ win shares represents an exceptional, historic season. For pitchers, Win Shares levels are typically lower—in fact, they often come close to mirroring actual wins.
Win shares differs from other sabermetric player rating metrics such as Total player rating and VORP in that it is based on total team wins, not runs above replacement.
Criticism of win shares
Players cannot be awarded "loss shares", or negative win shares, by definition. Some critics of the system argue that negative win shares are necessary. In defense of the system, proponents argue that very few players in a season would amass a negative total, if it were possible. However, critics argue, when one player does amass a negative total, he is zeroed out, thus diminishing other players' win-share totals. In an attempt to fix this error, some have developed a modified system in which negative win shares are indeed possible.
The allocation of win shares 48% offense and 52% defense is justified by James in that pitchers typically receive less credit than hitters in win shares and would receive far too few win shares if they were divided evenly.
One criticism of this metric is that players who play for teams that win more games than expected, based on the Pythagorean expectation, receive more win shares than players whose team wins fewer games than expected. Since a team exceeding or falling short of its Pythagorean expectation is generally acknowledged as chance, some believe[who?] that credit should not be assigned purely based on team wins. However, team wins are the bedrock of the system, whose purpose is to assign credit for what happened. Win shares are intended to represent player value (what they were responsible for) rather than player ability (what the player's true skill level is).
Within the sabermetric community there is ongoing debate as to the details of the system. The Hardball Times has developed its own Win Shares, as well as a number of derivative statistics, such as Win Shares Above Bench, Win Shares Percentage, Win Shares Above Average, and All Star Win Shares.
Basketball
Win shares has recently been applied sabermetrically to basketball players as well as baseball players. |
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