The Good Phight: Homefield Advantage

It appears as though homefield advantage is not a persistent thing—the Phillies have not squandered homefield advantage and the Rays have not capitalized on it for any specific reason and there is no reason to expect that the Phillies will have a weaker homefield advantage next year than the Rays.

So what does cause homefield advantage and can teams learn to exploit it—or keep other teams from exploiting their own?  For one thing, the correlation in between winning percentage and homefield advantage is strongly negative, -.190, and significant at the 97confidence level!  That means that there is only a 3% chance of getting a value so far away from 0 by random chance.  In other words, homefield advantage probably entails a disability on the road more than an advantage at home.