What value is the home field advantage for American football?

In the National Football League (NFL), the consensus is that the home field advantage is about three points. The actual value of the advantage is closer to 2.7 points, but there are some teams that have a more distinct advantage at home, and also some that have less of one.
The best team all-time, by far, is the Baltimore Ravens, who have a home field advantage (using scoring records of home and any games all time) of 4.5 points. Other teams with significant advantages above the statistical mean are the Buffalo Bills (3.7), the Minnesota Vikings (3.6), the Arizona Cardinals (3.6), and the Denver Broncos (3.5). The Vikings home field advantage in the cold has been nullified now, though, with their new stadium.
One of the teams in that top five, the Broncos, has a distinct geographical difference from the other teams in the NFL. Denver plays at an altitude of one mile (5,280) feet, something that opposing teams have sometimes found difficult to deal with, as the air is slightly thinner. It is also on the edge of the Rocky Mountains, so it snows a lot from October until the end of the season.