Mass killings in the United States may be contagious, according to a study Thursday that found each deadly tragedy can increase the likelihood that another will soon follow.

Scientists examined data from 1998 to 2013 on school shootings and other mass killings in the United States, according to the findings in the journal PLOS ONE.

Events in which four or more people died “create a period of contagion that lasts an average of 13 days,” said the study.

“Roughly 20 to 30 percent of such tragedies appear to arise from contagion.”

The risk of a follow-on shooting was temporary and appeared to fade after the two-week mark.

“The hallmark of contagion is observing patterns of many events that are bunched in time, rather than occurring randomly in time,” said lead author Sherry Towers, research professor in the Arizona State University’s Simon A. Levin Mathematical, Computational and Modeling Sciences Center.

Mass killings with firearms occur on average every two weeks in the United States, and school shootings tend to occur about once a month, according to background information in the article.

bbabo.Net