A study with season-by-season home field advantage data

Another home field advantage article from the April, 2005 "Journal of Sports Sciences":

This one is "Long-term trends in home advantage in professional team sports in North America and England (1876-2003)," by R. Pollard and G. Pollard. There's not much statistical analysis here, but it gives tables for year-by-year HFA data for the four major sports (including AL and NL separately), as well as for the four levels of English soccer. So if you need to know what the home winning percentage was for the 1966-67 NHL, you can look it up here (.606).

The authors note that for every sport, the HFA was highest in the early years of the respective league. They suggest travel as the explanation. Also, there was a large decline in English Football following the sport's seven-year hiatus during WWII – home winning percentage instantly dropped from the high .600s to the low-to-medium .600s. The authors mention players' loss of familiarity with the stadiums as one possible cause, but you get the impression they don't really believe strongly in that explanation. In any case, the HFA remained permanently lower, which wouldn't have happened if the cause was a temporary adjustment to the home stadiums.

Notable is that home field advantage in the NHL dropped significantly in the last 40 years or so. It was about .600 around 1970, then fell steadily to the .540s today. Any idea why? Maybe worse competitive balance? I suppose easier travel might also have something to do with it, but the other sports don't show it (although the NBA's HFA started dropping in the mid-80s).

Trivia: the highest season HFAs for the North American sports were:

NHL: .741 (1918-19, only 27 games played)
NBA: .749 (1950-51)
AL : .629 (1902)
NL : .655 (1877, only 177 games played)
NFL: .667 (1940, only 51 games played)