## Monday, 4 January 2016

### Bill James, Log 5 and HFA.

A rare NFL post simply to point out the genius of Bill James and how his work is applicable to many sporting contests, particularly during the NFL post season.

Many will know of his log 5 method to estimate the chance of Team A beating Team B if we have an opinion about the winning percentages of each side.

Invariably the calculation provides a winning match probability at a neutral venue and the home field advantage is bolted on afterwards.

However, HFA can be integrated into James' formulae, although it does become rather unwieldy, as you can see below.

Prob that Team A wins match = ((Team A true win%) * (1 – Team B true win%) * HFA)/((Team A true win%) * (1 – Team B true win%) * HFA +(1 – Team A true win%) * (Team B true win%) * (1 – HFA))

HFA is around 0.57 in the NFL and James' Pythagorean expectation, using an exponent of 2.37 and each teams points scoring and conceding record during the regular season can be used as the true talent to begin to frame post season odds during the run to the Super Bowl.