Stat of the Week: Log-5

“Log-5” is a method introduced by Bill James to predict the probability of victory when two teams of a given winning percentage play against each other. The formula is:

WPct = A – ( A x B ) / (A + B) – ( 2 x A x B )

Where “A” is Team A’s winning percentage, and “B” is Team B’s winning percentage. In the simplest terms, this formula indicates how often Team A should beat Team B.

Imagine that Team A wins 50% of its games and Team B wins 38% of its games. Inputting these percentages (as a decimal) into the formula above would yield:

WPct = 0.31/ (0.88) – (0.38) = 0.62

Or, in other words, Team A should beat Team B 62% of the time.