Minnesota Nice refers to the stereotype of Minnesotan residents to be mild mannered, helpful, and generous hosts. Minnesotans are believed to know their neighbors, help one another out, and to be polite yet reserved to strangers.
All states have a mix of nice and less-than-nice residents, but are there more nice Minnesotans than the rest of America?
The journal Perspectives on Psychological Science claims that Minnesota is nicer than the rest of America. Researchers studied psychological profiles of people across America, and analyzed the "big five" personality traits to find out which ones were more prevalent in different states.
In a piece on the results of the survey, the Wall Street Journal reported that Minnesota scored highly on agreeableness and extroversion. Minnesotans were around average in conscientiousness. Minnesota residents were some of the least neurotic and also some of the least open.
So if the scientists are to be believed, the average Minnesotan is indeed agreeable and reserved, just as the Minnesota Nice stereotype holds.