Research on inequality usually looks at fairly static social structures like schools, transport, healthcare, or jobs. But sometimes glaring inequality can be quite fleeting, as researchers Katherine DeCelles and Michael Norton argue in a recent PNAS article. Their example? Coming face to face with just how awful airplane economy class is in comparison to first class.

DeCelles and Norton wanted to study whether exposure to this kind of inequality could prompt people to behave badly. They looked at records of “air rage” incidents, where “abusive or unruly” passengers threaten staff or fellow travelers. “Popular explanations for air rage include crowded planes, frustrating delays, and shrinking seats,” they write—but they suspected these explanations are missing something.

They suggest that when people fly in economy class, their position in the social hierarchy becomes glaringly obvious. This fact is especially so if they have to walk through the first class section of the plane to get to their assigned space in a cramped hell.

It’s this reminder of occupying a low place in the pecking order that makes people act out, they write: “Exposure to these forms of inequality can trigger antisocial behavior." The researchers think it’s likely to cause a problem for first class passengers, too. Previous research has suggested that downward social comparisons can bring out nasty behavior in advantaged individuals, so they propose that first class passengers who watch economy class passengers traipse through the cabin might also be more prone to obnoxious behavior.

When DeCelles and Norton looked at all the air rage incidents reported by an anonymous airline over millions of flights, they found evidence for both of these hypotheses—along with indications of how factors like flight delays increase the risk of air rage. On flights with a first class cabin, the chance of an air rage incident was 3.84 times greater than on a flight without one. That's about the same increase in risk as a flight with a 9.5 hour delay.

If the passengers boarded from the front of the plane and walked through first class rather than directly into economy class, the chance of an economy class incident was 2.18 times greater. But this pales in comparison to the rage that having the riff-raff wander through their cabin apparently causes first class passengers: the chance of a first class air rage incident on front-boarding flights was 11.86 times greater.

This research might have bearing on bigger questions. If DeCelles and Norton are right, it would mean that researchers need to include a new factor in their thinking about inequality. For instance, criminologists who study the impact of social class on violent crime rates might also need to look at how visible inequality is made in different contexts.

As always, the results will need to be replicated in other research. However, even if it does replicate with data from other airlines, the explanation offered by the authors needs a lot more evidence. What the research shows is that something to do with first class—whether just having a first class cabin on board or actually walking through it—is related to a higher rate of air rage. But there's a black box in between that apparent cause and the extra rage that still needs to be explained. A reminder of social inequality is one possibility for what’s in the box, but there are other options.

For instance, the discomfort of crowds, delays, and cramped conditions (not to mention screaming children, tinny music leaking from headphones, and interesting smells) could also become more salient after witnessing the calm and luxury of first class. Becoming aware of how comfortable flying could be might make those discomforts harder to ignore. To really settle on an explanation, it's necessary to manipulate the possibilities so that we can tease apart the effects of inequality from pure physical discomfort.

PNAS, 2016. DOI: 10.1073/pnas.1521727113 (About DOIs).