“It’s so efficient,” Geoff Schwartz, a former N.F.L. lineman and Sirius XM commentator, said of the travel routines. Little gets overlooked, including how players combat inflammation on long flights. “Guys wear compression tights or they eat better. They’re just so much better trained and more in tune with their bodies.”

The Seattle Seahawks are this year’s favorite road warrior. After winning at Philadelphia last Sunday, the Seahawks improved to 8-1 on the road. At home at CenturyLink Field the Seahawks were 4-4, even though the stadium is designed to harness crowd noise so effectively that, at one point this season, an opposing lineman was flagged for unnecessary roughness because he couldn’t hear the referees whistle the play dead.

“It’s harder to play when you can’t hear. That’s a fact,” Coach Kyle Shanahan of the San Francisco 49ers said this week. “But that definitely doesn’t mean you can’t win, as everyone proves each week.”

To be sure, any attempts to find a surefire trend of a declining home field advantage can be a fraught endeavor that might depend on the size of the sample being studied. For instance, home teams have won 75 percent of divisional round games since 2010 — and 74 percent since 1990 — so maybe hold off on betting the farm on the Seahawks, the Vikings, the Titans or the Texans. Also, studies have shown even random outcomes can be streaky. Flip a coin 20 times and don’t be surprised if it comes up tails seven times in a row.

Yale economist Tobias Moskowitz said the psychology of the referees may be the most likely factor contributing to the winnowing of the home-field advantage.

Crowds have only a modest effect on professional athletes’ performance over time, Moskowitz said. N.B.A. free-throw shooting percentages are about the same at home and away, “down to the decimal point,” he noted. But when fans were barred from attending games in Italy’s top soccer league, Serie A, after an outbreak of violence in 2007, the home-field advantage fell by 80 percent.