Sabermetrics and NFL Referee Statistics: Home Field Advantage

Browsing the web, someone has posted on his blog about sabermetrics and home field advantage, suggesting that perhaps statistical analysis might shed light on whether a great deal of home field advantage is based on referees' unconscious bias toward the home team.
http://sabermetricresearch.blogspot.com/2007/02/how-much-of-home-field-advantage-is.html

Post a blog comment if you have some ideas for how to research this for NFL statistics.

I'll take a look through the statistics that I've been tracking in 2006 and 2007 to see what I can come up with. Maybe if someone is tracking field goal percentage by home and visiting teams that would help. Or better yet, adjusted-field-goal-percentage to even out how some field goals are harder to make than others.

Or to make things even easier, maybe if someone has kept track of extra point conversion percentage by home and visiting teams for a few NFL seasons?