Originally Posted by
Justin7
How about a different, simpler approach. Forget complex formulas.
Assume that the homefield advantage is worth X points. Use straightforward conversions. So if a 10-point favorite wins 80 % of the time on a neutral field, it becomes a 7-point favorite on the road. Conversions (for NFL) = 72% win rate.
Going the other way... a 10-point favorite becomes a 13 point favorite, and its win rate goes up to 85% (if you assume the conversion is accurate).
Perhaps you can do the conversion with a formula, but it seems much easier to do it. I don't know that you lose any accuracy this way either. I've tried a lot of ways to model for HFA, and I have never found anything better than a straight spread adjustment (although the adjustment changes substantially at the end of the year).