In the wake of the election, it’s clear American society is fractured. Negative emotions are running amok, and countless words of anger and frustration have been spilled. If you were to analyze this news outlet for the ratio of positive emotional words to negative ones, would you find a dip linked to the events of the past few weeks?

It’s possible, suggests a study published last week in Proceedings of the National Academy of Sciences. Analyzing Google Books and The New York Times’s archives from the last 200 years, the researchers examined a curious phenomenon known as “positive linguistic bias,” which refers to people’s tendency to use more positive words than negative words. Though the bias is robust — and found consistently across cultures and languages — social scientists are at odds about what causes it.

In this study, the authors shed light on some possible new patterns behind the effect. Across two centuries’ of texts, they found that people’s preference for positive words varied with national mood, and declined during times of war and economic hardship.

“It’s been shown that linguistic positivity bias exists, over and over again. What people haven’t actually looked at is how this phenomenon fluctuates over time, and whether there are certain predictors for it,” said Morteza Dehghani, a professor of psychology and computer science at the University of Southern California and an author of the paper.