The researchers involved in the state-by-state study attribute the seeming narcissistic behavior of residents to a few factors: that state history is often drilled into residents in school, that people are bad at math when it comes to estimating with small numbers, and a psychological tendency in people to think of themselves as better than average and to associate themselves with successful groups.

In a second study also published last month, some of the same researchers applied this approach on a global scale, asking residents in 35 countries how much their nation contributed to world history.

The results showed an even stronger phenomenon of collective narcissism at play. With 195 countries in the world, residents in every country surveyed had astronomically high estimations of their role in world history.