Historical results of picking the home team

Here's a graph of the home team winning percentage, for NFL games (and AFL, prior to 1970), from 1960 to 2007.

Click on the image to open a full-sized version

A few things stand out:

• From 1960 to 1976, only 4 years (1963, 1969, 1970, and 1973) are above the mean. There were 4 really bad years (1962, 1965, 1968, 1972). There were only two relatively good years (1969 and 1973). From 1974-2007, the worst year was 2006 (53.9%).

• Since 1986, the year-to-year difference has been in the range -5% < δ < +5%.
  . From 1960 to 1986, there were 11 swings of 5% or wider, including three (1968 to 1969: +13.3%, 1972 to 1973: +12.1%, and 1985 to 1986: -9.8%) of 9.8% or wider.

• It is surprising to me that the home-team winning percentage varies so much, even in the modern era. For a 267 game season (256 regular season and 11 playoff games), a 10% swing represents nearly 27 games.

  The disadvantages of being a road team seem pretty static: they still have to spend time travelling, they still have to spend time away from home, away from familiar comforts, away from team facilities...