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Primate Studies — Where BTF's Members Investigate the Grand Old Game Monday, August 19, 2002Win Values: A New Method to Evaluate Starting Pitchers  Part 6 Part
1: Introduction David Wells in AL 2000In this section I will provide the details of the Win Value calculation for a specific pitcher.? Doing so will allow the reader to gain a greater appreciation of the method.? David Wells in 2000 is the example I will use.? Wells went 208 for the Toronto Blue Jays and led the league in wins, despite a 4.11 ERA.? WAA, based largely upon Wells? fairly high ERA, is 2.1.? Win Values is able to evaluate Wells? season on a gamebygame basis, so is better able to give a more accurate evaluation of Wells? contributions to the Blue Jays that season.? Wells accumulated a 3.33 Win Value since he did a good job of ?managing? the runs support he received each game. Table 8: David Wells? 2000 GamebyGame Win Values>
*?? Z is the last inning David Wells appeared in; so that partial innings, including facing one or more batters without recording an out, count as a full inning.? ** The score is at the conclusion of both halves of the Zth inning; my method evaluates performances by the whole inning, not halfinnings. Let me describe Wells? first game to make sure the reader understands the method and what is being reported in the table.? The first row indicates that Wells started at home against Kansas City on April 3.? Wells lasted into the 7th inning, and the score at the conclusion of the 7th inning was 42 in favor of Toronto.? By using the empirical probabilities of winning when leading by a certain number of runs at the conclusion of the 7th inning, together with the ?could have been? run scored smearing probabilities, I estimate that Toronto had a .776 chance of winning that game based upon the score at the conclusion of the 7th inning. The next column of the table asks what was the probability that Toronto would win a game given that it had scored 4 runs at the conclusion of the 7th inning, with league average pitching.? By using the empirical probabilities of winning when scoring a certain number of runs at the conclusion of the 7th inning, together with the ?could have been? run scored smearing probabilities, I estimate that Toronto had a .502 chance of winning such a game with league average pitching. The Park Adder is reported in the next column.? In 2000, Toronto?s home park was a slight hitters park.? The Park Adder of .013 is based upon the park factor, the number of innings Wells pitched, and the number of runs Toronto scored in those innings.? As described above, the Park Adder is an estimate of the additional win probability differential of Wells? contribution given that the game that day was in a slight hitters park. The final column gives the Win Value for each game.? It is the estimate of the additional win probability that Wells contributed that day over what a league average pitcher would have been expected to contribute.? Algebraically, the .286 Win Value for the April 3 game is .776 (the win prob of the game with Wells? performance if it were in a parkneutral setting) minus .502 (the win prob of the game with league average pitching if it were in a parkneutral setting), plus .013 (the additional win prob differential due to the effect of the home park).? Wells? Win Value for the season is simply the sum of the Win Values for each of his starts. The game that Win Values deems to have been Wells? largest contribution (.621) during the season was the April 8 game at Texas.? Wells pitched a complete game shutout and the Blue Jays beat the Rangers 40.? The game that Win Values deems to have been Wells? worst contribution (.446) was his last start of the season on October 1 at Cleveland.? Wells was knocked out in the third inning, at the conclusion of which the score was 72 in favor of the Indians.? It may be interesting to note that Wells also received a significant negative Win Value (.415) for a game in which he was the winning pitcher.? On June 17, at Fenway Park the Blue Jays and Red Sox engaged in a classic slugfest.? Ramon Martinez started for Boston but was knocked out in the 4th inning.? David Wells lasted a little longer, but was knocked out in the 7th inning with Toronto leading 1110, which turned out to be the final score.? The Win Value approach penalizes Wells for almost squandering what should have been a surewin (11 runs of run support).?

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