Your questions answered . . .
Copyright © 2008, Dwight Gill
Yes, the XERA formulas are quite easy to use in spread sheet form. They're equally useful (in relative terms) at other levels of play - minor leagues, college, high school . . .
No, the new XERA formula is not the direct result of a multiple linear regression, as such - but it was certainly influenced by that mathematical wonder!
Here are all the XERA-related formulas. Note: these are copyrighted. Feel free to use them for your own purposes, but, if you publish any of them, or the results of using any of them, you're required to acknowledge the copyright, and that each formula was developed by Dwight Gill of Sarasota/Bradenton, FL.
To calculate XERA data for Hitters:
1) IP = INT (((AB * .344 + CS * .414 - H * .329) * 3) + .5) / 3 INT = The integer value of . . .
2) (Expected) ER = H * .200 + 2B * .55 + 3B * .656 + HR * 1.368 + (BB + HP) * .1846 - SO * .1177 + SB * .2116 - CS * .38
Expected ER * 9 / IP = XERA
To calculate XERA data for Pitchers:
1) AB = INT ((IP * 2.8345 + H * .9444 + SO * .068 - BB * .04) + .5)
2) (Expected) ER = H * .273 + BB * .111 + HR * 1.908 - SO * .0885
Expected ER * 9 / IP = XERA
3) SLG = (H * 1.188 + HR * 3.361) / AB
4) OBA = (H + BB + HP) / (AB + BB + HP)
Everything else is calculated using conventional (traditional) methods.
Team vs team probability: Let's say that team D has a record of 50 - 40 while team C, against similar competition, has a record of 48 - 42. Then (50 x 42) / (40 x 48) = 2100 / 1920 = 1.09375. [(D's wins x C's losses) divided by (D's losses x C's wins)] That number divided by that-number-plus-one (2.09375) = 1.09375 / 2.09375 = .522388 . . . meaning that team D would, typically, have a 52.2388% likelihood of beating team C. Dwight's evaluations give equal weight to the teams actual records and their would-be records based on runs squared. That weighted winning probability is then plugged into a Binomial Distribution. All our systems are based on precise mathematical applications, not subjective opinions.
Projected Wins simply applies a team's current R2 percentage to the balance of its games, and adds that to its current record.
The Magic Number: In MLB, it's simply 163 - (A wins + B losses), that is, the total of wins by team A and losses by team B (generally, the team in second place), subtracted from 163. That same rule can be applied to any two teams in a division. If, for example, the first place team had 80 wins sometime in September, and your team was in fourth place with 78 losses, then A wins would be 80 and B losses would be 78. So, 163 - 158 (80 + 78) = 5. That means that any combination of wins by the first place team, and/or losses by your team, that adds up to 5, would eliminate any possibility of your team overtaking the first place team this season. The Padres magic number was 1 at the end of the 2006 season. They won the NL West by the tie-breaker rule (in this case, beating the Dodgers in head-to-head competition during the regular season). Keep those cards and letters (and emails) coming! You can reach Dwight at xerastats@gmail.com.