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Originally Posted by DamnYankees
I'm sure its been asked, and its something jcato certainly has considered, but why does CatoBase not calculate winshares for past years?
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Why not? Well, this is probably why not. It's from:
http://www.baseballgraphs.com/details.html#sharecalc (I recommend that web site to you all)
"How are Win Shares calculated?
Okay, here's how Bill James calculates Win Shares. Ready?
First, you divide responsibility for a team's wins between the offense (batting and baserunning) and defense (pitching and fielding). You do this by calculating the team run differential through a method James calls Marginal Runs. You first calculate the average number of runs scored per team in the league. You next adjust your team's runs scored and runs allowed for the ballpark in which they played half their games (i.e. home games). Then you add together two figures: all runs scored over 52% of the league average (credited to the offense), and all runs allowed less than 152% of the league average (credited to the defense). This is total marginal runs.
Next, you take the percent of marginal runs contributed by the offense, multiply it by the number of wins times three. This is the total number of offensive Win Shares. You do the same thing for defensive Win Shares.
Next, you attribute offensive Win Shares to individual players. This is done through two key metrics: Runs Created and Outs Made. Runs Created is a formula built by James and refined over the years. It starts with the basic equation of OBP times total bases and then adds player credit for other factors, including stolen bases, caught stealing, grounding into double plays, batting average and home runs with runners in scoring position and the kitchen sink. Runs Created is calculated for every single batter, including pitchers (if they're in the National League).
Next, you subtract the league 'background' Runs Created (52% of the league average) from each player's Runs Created based on the number of Outs Made by that batter, adjust it for ballpark, and credit each player with the result; essentially individual marginal runs created. Add these up for all players and use each player's percentage of the whole to allocate offensive Win Shares to each. Note that any player whose Runs Created are less than 52% of the league average runs created per out is credited with no Win Shares. This doesn't happen very often (except for pitchers).
That was the easy part. Now you've got to deal with the defense. The first step is to divide defensive Win Shares between pitching and fielding. This done through a complicated formula that accounts for FIP elements that can be attributed only to pitchers (home runs, walks and strikeouts) as well as a team's DER (Defensive Efficiency Ratio, adjusted for the ballpark) and other fielding statistics such as passed balls, errors and double plays. Typically, about 70% of defensive Win Shares are credited to pitching, and 30% to fielding. The Win Shares system is bound so that pitching never is credited with less than 60%, or more than 75%, of defensive Win Shares.
Next, you allocate pitching Win Shares to individual pitchers. This is accomplished through an even more complicated formula that starts with each pitcher's marginal runs not allowed (same approach as team marginal runs not allowed), wins, losses and saves. Special consideration is given to relievers by estimating the number of high-leverage innings they pitched (ninth innings with one-run leads are more important than first innings with no score) and something called "Component ERA" which is essentially ERA re-calculated according to the actual underlying run elements.
Finally, pitchers are deducted Win Shares if they are absolutely lousy hitters. Call this the "Dean Chance" factor. All these elements are then mixed together in a complicated formula to allocate pitching Win Shares to individual pitchers. As in offensive Win Shares, any pitcher who gives up more than 152% of league-average Runs Scored (adjusted for ballpark) does not receive any credit for pitching Win Shares.
One note: responsibility for unearned runs is split 50/50 between pitching and fielding.
Which leads us to the next, most complicated step: allocating fielding Win Shares to fielding positions, and then to individual fielders. The calculations differ for each position. Essentially, James has selected four defensive statistics to evaluate positions. Here they are by position, listed in order of importance:
Catchers: Caught Stealing, Errors, Passed Balls and Sacrifice Hits Allowed
First Basemen: Plays Made, Errors, Arm Rating and Errors by third basemen and shortstops
Second Basemen: Double Plays, Assists, Errors and Putouts
Shortstops: Assists, Double Plays, Errors and Putouts
Third Basemen: Assists, Errors, Sacrifice Hits Allowed and Double Plays
Outfielders: Putouts, Team DER, Arm Elements and Assists and Errors
Lots of things to note about the fielding calculations.
First, the statistics are adjusted based on the number of innings a lefthander pitches for the team, which has an impact on which side of the field batters hit the ball to.
Second, these stats are calculated as a proportion of the team's total, divided by the league-average proportions of the total. In other words, if a shortstop has 50 assists and his team has 100 assists in total, he receives just as much credit as the shortstop who has 100 assists and plays on a team with 200 assists in total. This is important, because it adjusts the fielding stats for the fact that fielders may be playing behind pitchers with certain tendencies such as giving up more ground balls vs. fly balls.
Third, double plays are only factored in as a proportion of potential double plays. If teams don't have a lot of runners on first, they have less of a chance to turn double plays, and Win Shares takes this into account.
Fourth, team DER is used to credit outfielders with fielding Win Shares because it is James' observation that outfielders have a much larger impact on DER than infielders. James acknowledges that there is some 'circular logic' here.
Fifth, there is a final element included in the formula to allocate fielding Win Shares to individual fielders. This element is called 'Range Bonus Play.' It particularly impacts outfielders in the following manner: if one outfielder handles more opportunities per inning played than the other outfielders on the team, he will be credited with more fielding Win Shares. This especially impacts centerfielders, who typically handle more chances per inning played than the corner outfielders."
That's not a small undertaking and it requires a *lot* of data.