The Baseball Gauge Glossary
Win Shares are calculated using the formula in the book Win Shares by Bill James. If you don't have the book and would like to take a look at the calculations, "Patriot" has a very detailed seven part walk through on his site.
If you are wondering why the Win Shares totals do not exactly match those totals in the Win Shares Book, there are a couple of reasons:
The first, and possibly the biggest reason is that this site uses different park factors than Bill James did. Any difference in park factor can alter the distribution of offensive and defensive Win Shares as well as other parts of the formula.
Possibly, the second biggest reason is that this site keeps decimal points, where as Bill James rounded to the whole number. This is done to keep the values as accurate as possible.
Next, when figuring Catcher's claim points, the book only uses opponent's stolen base data from 1987 until present. This site uses this data from 1954 until present. On the flip side, the book uses sacrifice allowed data from 1931 until present, while this site only uses it from 1956 until present. This difference in data available will alter catcher claim points, which will also slightly alter the other positions as well.
When calculating Runs Created for offensive Win Shares, the same RC formula is used except for that RISP data is not included.
When calculating Pitching Win Shares, the book includes an adjustment for pitchers hitting below a certain level. This site does not make that adjustment since a pitcher's offense (or lack of) should not affect his pitching Win Shares.
Finally, Catcher's ERA is not included in calculating claim points. This is done mainly because of lack of data available, but also because of possible inaccuracies. Some pitchers use a "personal" catcher, which will cause the games caught for each pitcher to be unequal. For example, Eddie Perez was Greg Maddux's personal catcher while Javy Lopez caught the majority of the other games. It is inaccurate to compare their catcher's ERA's since they caught different pitchers.
Per 162 Games
The rate of a statistic over the course of 162 games. This is based on the player's entire career. Position players and pitchers games played are treated differently.
Batting Seasons = Games appeared as a position player divided by 162. (G / 162)
Pitching Seasons = Games appeared as a pitcher plus Games Started, divided by 68. ((G + GS) / 68)
Seasons = Batting Seasons + Pitching Seasons
Total = Career Total in that statistic
per 162 = Total / Seasons
Developed by Jay Jaffe in 2004 at Baseball Prospectus. It is meant to gauge a player's Hall of Fame credentials by comparing them to Hall of Famers at the same position. JAWS is the average of a player's career total Win Shares and the total of their seven best seasons (peak).
Since not all positions are represented equally in the Hall of Fame, JAWS requires a minimum # of players at each position. Currently, the position with the most players in the Hall of Fame is RF, with 25. To meet the required minimum, the calculation includes the average position player's JAWS score for each player that it is short of the minimum (Starting and Relief Pitchers are not subject to this minimum requirement).
For example, there are currently 15 catchers in the Hall of Fame, which is 10 players short of the minimum. The JAWS calculation will find the average of the 15 catchers AND 10 average Hall of Fame position players to determine the average Hall of Fame catcher's JAWS score.