Reports of domestic violence increased by 10 percent in areas where the local National Football League team lost a game it was expected to win.

“The study is about how emotional cues affect people’s behavior,” economics professor Gordon Dahl said. “When people’s expectations are unmet, they get this emotional cue that makes them very upset and unfortunately translates into a horrible thing, which is increased domestic violence.”

Since football games evoke emotional investment, Dahl and UC Berkeley economics professor David Card examined 900 regular NFL games from 1995 to 2006 — comparing pre-game betting odds against eventual game results in a regular season for six NFL teams, which included the Denver Broncos, Kansas City Chiefs and New England Patriots. They compared predictions and results for the game to reports of domestic violence collected from the database of local police reports — the National Incident-Based Reporting System — in home cities of the teams.

Analysis of the reports demonstrated that the incidence of domestic violence was no different before the game had begun, or even during the first half of the game.

“Most of the violence is concentrated in a narrow window, in the last hour of the game and a couple hours afterwards,” Dahl said.

Yet research showed that unexpected loss produces a greater change than does the pleasant surprise of an unexpected win.

“Your happiness [is] relative to what you think is going to happen,” Dahl said. “Pleasant surprises don’t do much for us. When you are expected to lose but unexpectedly win, that doesn’t really reduce domestic violence.”

There is also no change in domestic violence when the team loses a game it was expected to lose, as there is less emotional investment in the game.

The spikes in violence were more prevalent when viewers were more emotionally connected to the game, such as during playoff contention or in games against traditional rivals.

Loss to a rival team when the team is in playoff contention results in a 17-percent increase in domestic violence, while upset losses to a non-rival team witnessed a rise of 8 percent.

“If the game is especially frustrating because you were hit with an unusual number of penalty yards, your quarterback was sacked an unusual number of times or if you were intercepted an unusual number of times — when those frustrating things happen, then we also [see] a larger spike in violence of about 15 percent,” Dahl said.