A newly published academic study looked into the factors that make air rage more or less likely to happen on any given flight – and the results were not what the researchers expected.

The researchers from the University of Toronto and Harvard Business School got access to internal reports on air rage over several years from “a large international airline,” and they found that the biggest predictors of passenger misbehavior fit right into the theme of a Bernie Sanders campaign speech.

While drunkenness, cramped seating, insufficient legroom and the other usual suspects all contributed to “antisocial behavior” on aircraft, the authors said, the biggest factor by far in predicting the likelihood of an incident was passengers’ “temporary exposure to both physical and situational inequality.”

Specifically, the study found that incidents of air rage in economy class were much more likely to happen on a flight that has a first class cabin than on one that doesn’t. The odds of an air rage incident were also higher when economy passengers had to pass through first class to get to their seats, rather than boarding directly to the middle of the plane. (The latter factor raised the odds of air rage in both first and economy classes, they noted.)

Flights with a first class cabin had an air rage incident rate of 1.58 per 1,000 flights, the study found – more than 10 times the rate for flights with no first class (0.14 per 1,000 flights). As for boarding, the odds of an incident in the economy cabin more than doubled when everyone boarded from the front of the plane.

One of the researchers told the Toronto Star that passengers don’t mind front-cabin flyers getting better treatment, but they don’t like it to be too obvious. “People have paid between several hundred dollars to several thousand dollars, and they don’t want to be made to feel like second-class citizens,” said the University of Toronto’s Katy DeCelles, an associate professor at the university’s Rotman School of Management.

She said airlines could probably reduce air rage by eliminating factors that make passengers more aware of the preferred treatment that first class passengers get – e.g., putting curtains between the cabins, using dual boarding areas, and making sure that meals being cooked in first class can’t be smelled in coach.

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