It’s not just millennials who are narcissistic, according to a new study out of the University of Michigan — it’s Americans in general.

In a study that reviewed “self-interest” in the U.S. by analyzing presidential State of the Union addresses from 1790 through 2012, researchers found that egotism and self-interest has been steadily increasing since the beginning of the 20th century. This so-called self-interest was higher during economic booms, and lower during tough times — such as the 2008-09 recession.

They examined the types of words used in State of the Union addresses, measuring the ones that related most to self-interest and others that were associated with care or concern for other people. “The focus seemed to be on the needs of other people, rather than on the needs and desire of the president or people close to him,” Sara Konrath, a social psychologist, said in a press release. Interestingly, self-interest was lower during the 1800s but increased during the 1900s.

“We found that self-interest trends tend to peak after economic booms,” William Chopik, an author of the study and a doctoral candidate in psychology, said in a news release. “In the 20th century, it peaked after World War II and again in the 1970s.” And during the 2008-09 recession, self-interest decreased, possibly because “the challenges facing the country increased the nation’s sense of togetherness and focus on the needs of others,” Chopik said.

The authors of the study wanted to understand self-interest trends, as self-interest “still motivates much of adult cognition and behavior, at least within Western cultural contexts,” they wrote in the introduction. Scientists have studied these trends before, finding that college-age students have developed increasing levels of “positive self-evaluation statements” since the 1960s. There have also been rising levels of narcissism, self-esteem, and “simultaneous decreases in empathy,” the authors wrote.

It was through the constructs of State of the Union addresses that researchers measured self-interest in this study. They found that words relating to “other-interest” — such as "his/her," or "neighbor" — decreased over time. Words relating to self-interest became more common, such as "I, me, mine," and "mother." But though these trends may be fairly obvious, it’s much more difficult to pinpoint the underlying reasons for it. “Historical changes are complex, and it is hard to point a finger at one specific cause,” Chopik said. It could possibly be due to an increase in prosperity among Americans, as well as a desire for security and instant gratification (augmented by the fast-paced technological and social media world).

Plenty of studies have delved into the link between social media and increased narcissism, blaming Twitter, Facebook, and Instagram for making jealousy, self-promotion and competition so ingrained in our day-to-day lives. But at least millennials can rest assured it’s not just them. “[T]here may also be more pressure to succeed over the past couple of centuries,” Chopik added. “In some ways, we’ve become a more competitive society, and perhaps what we’re seeing in presidential addresses is a reflection of this trend.”