A new study found that mass killings and school shootings inspire similar violent attacks for an average of 13 days after the initial tragedy. The study also that found mass shootings were significantly higher in states with a high rate of gun ownership.

The study was conducted by an Arizona State University team which examined four databases based on past high-profile mass killings and school shootings between 1998 and 2013. The data from a total of 897 events involving four or more deaths was fit to a contagion model to see whether the tragedies increased the odds of similar events occurring in the future. Using the model, the team found that mass killings and school shootings create “a period of contagion that lasts an average of 13 days,” adding that “roughly 20 to 30 percent of such tragedies appear to arise from contagion.”

RT