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The Log5 method is Bill James' name for a method of estimating the winning percentage when two teams meet, or the expected rates resulting from a batter/pitcher confrontation. While James developed the team method independently and the batter/pitcher method in conjunction with Dallas Adams, the team method is in fact equivalent to the Odds Ratio method and can be derived from Bayes formula.

Log5 for Teams[edit]

The expected winning percentage of team A versus team B is given by:

W%(A v. B) = W%(A)*(1 - W%(B))/(W%(A)*(1 - W%(B)) + (1 - W%(A))*W%(B))

Incorporating Home Advantage[edit]

To add a home-field/court/ice advantage term to the log5 formula, plug the expected probability of a home team winning an even matchup (for instance, .60 for the NBA, .55 for the NHL, .54 in MLB) into the following formula:

((Team A win%) * (1 - Team B Win%) * HA)/((Team A win%) * (1 - Team B Win%) * HA +(1 - Team A win%) * (Team B Win%) * (1 - HA))

Where Team A is the home team, Team B is the road team, and HA is the home advantage.