A new study published in the Nature Human Behavior journal has found that school shootings in the US increase as the economy slows and unemployment increases. Researchers at Northwestern University looked at a list of 381 school shootings between 1990 and 2013, and found two periods of increased gun violence in schools. "The timing of these periods significantly correlates with increased economic insecurity," researchers said.

"We spent days doing nothing but reading about violence at schools, which is quite possibly the saddest thing I’ve had to do for research,” said Adam Pah, Northwestern professor and lead author of the study.

The research team discovered an increase in shooting incidents at elementary and high schools between 1992 to 1994, as well as an increase in shootings at postsecondary schools from 2007 to 2013. During both of these time periods, the economy was faltering, causing unemployment to rise.

"The link between education and work is central to our expectations about economic opportunity and upward mobility in America," said John Hagan, professor of sociology at Northwestern and co-author of the study. "Our study indicates that increases in gun violence in our schools can result from disappointment and despair during periods of increased unemployment, when getting an education does not necessarily lead to finding work."